Printed circuit board

ABSTRACT

A printed circuit board includes a chip capacitor having electrodes and a metal film formed on one or more of the electrodes, an accommodating layer accommodating the chip capacitor inside the accommodating layer, a connection layer formed over the accommodating layer and having a via hole opening extending to the metal film, and a first via hole structure formed in the via hole opening of the connection layer and connected to the metal film on the one or more of the electrodes of the chip capacitor.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation of and claims the benefit of priorityunder 35 U.S.C. §120 from U.S. Ser. No. 11/928,397, filed Oct. 30, 2007,which is a continuation of U.S. Ser. No. 11/062,672, filed Feb. 23,2005, now U.S. Pat. No. 7,307,852, which is a divisional of U.S. Ser.No. 09/830,361, filed Apr. 25, 2001, now U.S. Pat. No. 6,876,554, whichis a national stage of International Application No. PCT/JP2000/05972,filed Sep. 1, 2000. This application further is based upon and claimsthe benefit of priority under 35 U.S.C. §119 from the prior JapanesePatent Application Nos. 11-248311, filed Sep. 2, 1999, 11-360306, filedDec. 20, 1999, 2000-103730, filed Apr. 5, 2000, 2000-103731, filed Apr.5, 2000, 2000-103732, filed Apr. 5, 2000, 2000-103733, filed Apr. 5,2000, 2000-221349, filed Jul. 21, 2000, 2000-221351, filed Jul. 21,2000, 2000-221352, filed Jul. 21, 2000, 2000-221353, filed Jul. 21,2000, and 2000-221354, filed Jul. 21, 2000.

TECHNICAL FIELD

The present invention relates to a printed circuit board on whichelectric elements, such as IC chips, are mounted. More specifically, thepresent invention relates to a printed circuit board incorporatingcapacitors therein, and a method for manufacturing the same.

BACKGROUND ART

In a computer, the length of electric wiring between the power supplyand the IC chip is usually long, and therefore, the loop inductance atthis electric wiring is extremely large. The variation in the voltage atwhich the IC is driven in high-speed operation mode becomes very largeaccordingly, possibly causing malfunction of the IC. In addition, itbecomes difficult to stabilize the voltage of the power supply. In anattempt to avoid these troubles, a capacitor is mounted on the surfaceof the printed circuit board as an auxiliary device for assisting thepower supply operation.

Specifically, the loop inductance which causes the variation in voltagedepends on the length of electric wire from a power supply shown in FIG.72(A) to a power supply terminal 272P of an IC chip 270 through a powersupply line in a printed circuit board 300, and the length of electricwire from a ground terminal 272E in the IC chip 270 to the power supplythrough a ground line in the printed circuit board 300 from the powersupply. The loop inductance can be reduced by narrowing the distancebetween the electric wires through which a current in a reversedirection to each other flows, for example, the distance between thepower supply line and the ground line.

Therefore, as shown in FIG. 72(B), a chip capacitor 298 is mounted onthe surface of the printed circuit board 300, thereby shortening thelength of electric wire between the power supply line and the groundline in the printed circuit board 300 which connects the IC chip 270 tothe chip capacitor 292 to be the power supply source, as well asnarrowing the distance between the electric wires.

However, the degree of the voltage drop, which causes the variation inthe IC driving voltage, depends on the frequency at which the IC chip isdriven. As the frequency at which the IC chip is driven increases, itbecomes impossible to reduce the loop inductance even if the chipcapacitor is mounted on the surface of the printed circuit board 300 asis conducted in the case shown in FIG. 72(B). As a result, it becomesdifficult to sufficiently suppress the variation in the IC drivingvoltage.

In this situation, the present inventors have conceived to mount a chipcapacitor inside the printed circuit board. As a method for embedding acapacitor into a substrate, techniques described in Japanese UnexaminedPatent Publications Nos. 6-326472, 7-263619, 10-256429, 11-45955,11-126978, 11-312868 and the like may be employed.

Japanese Unexamined Patent Publication 6-326472 discloses a technique inwhich a capacitor is embedded in a substrate made of resin such as glassepoxy. This structure reduces the noise in the power supply, andeliminates the need of the space for mounting the chip capacitor,thereby reducing the size of insulating substrate. Japanese UnexaminedPatent Publication No. 7-263619 discloses a technique in which acapacitor is embedded into to a substrate made of ceramics or alumina.The capacitor is connected between the power supply layer and the groundlayer. This structure shortens the length of electric wire and reducesthe inductance of the electric wire.

However, these prior art techniques described above cannotsatisfactorily shorten the distance between the IC chip and thecapacitor, and also cannot reduce the inductance at the higher frequencydomain of the IC chip to a level required at present. In particularly, abuildup multi-layer printed circuit board made of resin has problemssuch as disconnection between the terminal of the chip capacitor and thevia hole, the peeling of the chip capacitor from the interlayer resininsulating layer, and the generation of cracks in the interlayer resininsulating layer, resulted from the difference in thermal expansioncoefficients between the capacitor made of ceramics, and the coresubstrate and the interlayer resin insulating layer made of resin. Theseproblems hinder the printed circuit board from having high reliabilityover a long period of time.

The present invention has been made to solve the above-describedproblems of the prior arts, and the objective thereof is to provide aprinted circuit board capable of reducing a loop inductance and havinghigh reliability, and a method for manufacturing the same.

DISCLOSURE OF THE INVENTION

In order to achieve the above purpose, a printed circuit board ischaracterized by comprising a core substrate, and a resin insulatinglayer and a conductor circuit laminated on the core substrate, wherein acavity is formed in the core substrate, and a plurality of capacitorsare accommodated in the cavity.

In the printed circuit board, a large cavity is formed in a coresubstrate, and a plurality of capacitors are accommodated in the cavity.With this arrangement, a plurality of capacitors can be reliablyprovided within the core substrate. The capacitors can be provided atplaces close to each other in the cavity, the package density of thecapacitors can be increased. Since a plurality of capacitors are mountedwithin the cavity, the plurality of capacitors are aligned to the sameheights with each other. A resin layer can be formed on the coresubstrate into a uniform thickness, and via holes can be stably formed.Since the cavity is formed in such a manner as to have a large area, thecapacitors can be provided at accurate positions. As a result, aninterlayer resin insulating layer and a conductor circuit can beproperly formed on the core substrate, thereby lowering the rate ofgenerating defective printed circuit boards.

The cavity is preferably filled with a resin. The resin eliminates aspace between the capacitors and the core substrate. As a result, thebehavior of the capacitors incorporated in the core substrate becomessmall. In addition, even if the stress is generated caused by thecapacitors, the stress can be alleviated by the resin charged in thespace. The resin also has an effect of adhering the capacitors to thecore substrate, and lowering a migration between the capacitors and thecore substrate.

A resin may be charged between the capacitors in the cavity. With thisarrangement, the capacitors can be fixed in the cavity after decidingtheir positions in the capacitors. The thermal expansion coefficient ofthe resin is made to be smaller than a thermal expansion coefficient ofthe core substrate, that is, is set to the value close to that of thechip capacitor made of ceramics. In this manner, even if internal stressis generated between the core substrate and the capacitors caused by thedifference in the thermal expansion coefficients therebetween, cracksand peelings do not easily occur in the core substrate. As a result,high reliability can be attained. In addition, no migration isgenerated, and the connection with the capacitors is stabilized.

A through hole may be formed between the capacitors in the resin layer,and a signal line does not pass through the chip capacitors. Thisstructure eliminates the problems that the impedance becomesdiscontinuous by the high dielectric body to generate a reflection, andthat the transmission is delayed by passing through the high dielectricbody.

The through holes enable the establishment of an electric connectionbetween the front surface and the back surface of the printed circuitboard. In addition, a wire can be provided below the capacitors throughthe buildup layer, and pins and BGAs for the capacitors can be provided.

An electric connection for electrodes formed with a metal film of thecapacitors may be established by via holes formed by plating. Theelectrodes of the chip capacitor are made by metallizing, and have pitsand projections on their surfaces. However, the surfaces become smoothby formation of the metal film, and the via holes are then formed on thesmooth surfaces. In this manner, when penetrating openings are formed inthe resin coating the electrodes, no resin remains, and a reliability ofthe connection between the via holes and the electrodes can beincreased. Furthermore, since the via holes are made by plating into theelectrodes formed with the copper plated film, the electrodes are firmlyconnected to the via holes. No disconnection occurs between theelectrodes and via holes even when a heat cycle test is conducted.

The metal film formed on the electrodes of the capacitors preferablyincludes any one of metals selected from the group consisting of copper,nickel, and noble metals. Tins and zinc are not preferable, because ifthe capacitors incorporated in the printed circuit board have a filmincluding these metals formed on their electrodes, a migration is easilygenerated at a connection with the via holes.

The surfaces of the chip capacitors may be roughened. The rough surfacecontributes to an increased adhesion between the chip capacitors made ofceramic, and a connection layer and a resin insulating layer made ofresin, thereby avoiding the resin insulating layer from peeling from theinterface with the chip capacitors even when a heat cycle test isconducted.

The chip capacitors may be accommodated in the printed circuit board inthe state where at least a part of the electrodes of each capacitor isuncoated with a coating layer and exposed to the outside. An electricconnection for the electrode exposed from the coating layer isestablished. The metal exposed from the coating layer includes copper asa main component, because the connection resistance can be lowered.

A chip capacitor in which electrodes are formed along an inside of theouter edge thereof may be used. With this arrangement, a large space canbe used for external electrodes even if a conduction is establishedthrough the via holes, and therefore, the broadened range of alignmentis allowed. As a result, a problem of disconnection is eliminated.

A chip capacitor in which electrodes are formed in matrix may be used.It becomes easy to accommodate a large chip capacitor in a coresubstrate. Therefore, it becomes possible to increase an electrostaticcapacity, and a problem concerning electricity can be solved. Inaddition, warpage is hard to generate in the printed circuit board evenif the printed circuit board undergoes various thermal histories.

A plurality of chip capacitors from each of which a plurality of piecesare to be obtained may be coupled into one piece unit and used. In thismanner, an electrostatic capacity can be properly adjusted and the ICchip can be properly operated.

A capacitor may be mounted on the surface of the printed circuit boardon top of the capacitors accommodated in the substrate. Since thecapacitors are accommodated within the printed circuit board, thedistance between the IC chip and each capacitor is shortened. Inaddition, the loop inductance can be lowered, and electric power can beinstantaneously provided. On the other hand, since a capacitor isprovided on the surface of the printed circuit board as well, acapacitor having a large capacity can be mounted. In this manner, largeelectric power can be easily supplied to the IC chip.

A method for manufacturing a printed circuit board is characterized bycomprising at least the following steps (a) to (c):

(a) forming a cavity in a core substrate;

(b) mounting a plurality of capacitors in the cavity; and

(c) charging a resin between the capacitors.

In the method, a large cavity is formed in a core substrate. With thisarrangement, a plurality of capacitors can be reliably provided in thecore substrate. In addition, since a plurality of capacitors are mountedin the cavity, the plurality of capacitors are aligned to the sameheights with each other. As a result, the surface of the core substratebecomes flat and smooth. In addition, the cavity is formed in such amanner as to have a large area, the capacitors can be located ataccurate positions. The interlayer resin insulating layer and theconductor circuit can be properly formed on the core substrate withoutimpairing the flatness and smoothness of the core substrate. Therefore,the rate of generating defective printed circuit boards can be lowered.In addition, a resin is charged between the capacitors, the capacitorscan be fixed in the cavity after the positions of capacitors aredetermined within the cavity.

A pressure may be applied to the upper surfaces of the plurality ofcapacitors in the cavity, or tapped to align the chip capacitors intothe same heights with each other. By this process, even if chipcapacitors having largely different sizes from each other are providedin the cavity, they are aligned into the completely same heights witheach other. As a result, the core substrate can has a flat and smoothsurface. The interlayer resin insulating layer and the conductor circuitas upper layers can be properly formed on the core substrate withoutimpairing the flatness and smoothness of the core substrate, andtherefore, the rate of generating defective printed circuit boards canbe lowered.

A through hole may be formed between the capacitors in the resin layer.A signal line does not pass through the chip capacitors. This structureeliminates the problems that the impedance becomes discontinuous by thehigh dielectric body to generate a reflection, and that the transmissionis delayed by passing through the high dielectric body. The throughholes enable the establishment of the electric connection between thetop and bottom surfaces of the printed circuit board. It is possible toprovide wires under the capacitors through the buildup layer, andtherefore, pins and BGAs of the capacitors can be provided.

A method for manufacturing a printed circuit board is characterized bycomprising at least the following steps (a) to (c):

(a) forming penetrating openings in a resin material having a corematerial impregnated with a resin;

(b) attaching a resin material to the resin material formed with thepenetrating openings to form a core substrate having a cavity;

(c) mounting a plurality of capacitors in the cavity of the coresubstrate; and

(d) charging a resin between the capacitors.

In the method, a large cavity is formed in a core substrate. With thisarrangement, a plurality of capacitors can be reliably provided in thecore substrate. In addition, since a plurality of capacitors are mountedin the cavity, the plurality of capacitors are aligned to the sameheights with each other. As a result, the surface of the core substratebecomes flat and smooth. In addition, the cavity is formed in such amanner as to have a large area, the capacitors can be located ataccurate positions. The interlayer resin insulating layer and theconductor circuit can be properly formed on the core substrate withoutimpairing the flatness and smoothness of the core substrate. Therefore,the rate of generating defective printed circuit boards can be lowered.In addition, a resin is charged between the capacitors, the capacitorscan be fixed in the cavity after the positions of capacitors aredetermined within the cavity.

A pressure may be applied to the upper surfaces of the plurality ofcapacitors in the cavity, or tapped to align the chip capacitors intothe same heights with each other. By this process, even if chipcapacitors having largely different sizes from each other are providedin the cavity, they are aligned into the completely same heights witheach other. As a result, the core substrate can has a flat and smoothsurface. The interlayer resin insulating layer and the conductor circuitcan be properly formed on the core substrate without impairing theflatness and smoothness of the core substrate, and therefore, the rateof generating defective printed circuit boards can be lowered.

Through holes may be formed between the capacitors in the resin layer,and thus a signal line does not pass through the chip capacitors. Thisstructure eliminates the problems that the impedance becomesdiscontinuous by the high dielectric body to generate a reflection, andthat the transmission is delayed by passing through the high dielectricbody. The through holes enables the establishment of the electricconnection between the top and bottom surfaces of the printed circuitboard. It is possible to provide wires under the capacitors through thebuildup layer, and therefore, pins and BGAs of the capacitors can beprovided.

In order to solve the above problem, a printed circuit board ischaracterized by comprising a core substrate, and a resin insulatinglayer and a conductor circuit laminated on the core substrate,

wherein the core substrate incorporates a connection layer formed by aninsulating resin layer including at least one or more layer, and anaccommodation layer accommodating a capacitor in its spot-faced section.

It means the circuit formed by buildup method where an interlayer resininsulating layer is formed on the core substrate, and via holes orthrough holes are formed in the interlayer resin insulating layer toform a conductor circuit as a conductive layer. As the buildup layer, asemi-additive method or a fully-additive method may be employed.

In the printed circuit board, capacitors are mounted within the printedcircuit board. In this manner, the distance between the IC chip and eachcapacitor is shortened, and the loop inductance can be lowered. The coresubstrate incorporates one or more connection layers and anaccommodation layer for accommodating the capacitors. Since thecapacitors are accommodated within the accommodation layer having largethickness, the thickness of the core substrate does not become large.The thickness of the printed circuit board does not become large even ifthe interlayer resin insulating layer and the conductor circuit arelaminated on the core substrate.

It is desirable to fill the cavity with a resin. As a result, thebehavior of the capacitors incorporated in the core substrate becomessmall. In addition, even if the stress is generated caused by thecapacitors, the stress can be alleviated by the resin. The resin alsohas an effect of adhering the capacitors to the core substrate, andlowering a migration between the capacitors and the core substrate.

An accommodation layer may be constituted by a resin substrate having acore material impregnated with a resin. As a result, sufficiently highstrength can be given to the core substrate.

The connection layer and the capacitors accommodated in theaccommodation layer may be connected to each other through a conductiveadhesive. In this manner, the electrical connection with the capacitorsand the adhesion between the capacitors and the connection layer can beassured. The conductive adhesive may be a material having bothconductivity and adhesiveness such as a solder (Sn/Pb, Sn/Sb, Sn/Ag,Sn/Ag/Cu), conductive pastes, and resins impregnated with metalparticles.

The space created between the conductive adhesive and the capacitor ispreferably filled with a resin, because, in this manner, the behaviorderived from the capacitors can be alleviated and the migration of theconductive adhesive can be prevented.

A circuit which is connected to the conductive adhesive may be providedbetween the connection layer and the accommodation layer. In thismanner, a connection with the capacitors can be reliably establishedthrough the circuit. By providing a circuit constituted by a metal layerbetween the connection layer and the accommodation layer, the warpage ofthe core substrate can be prevented.

An external substrate (i.e. daughter board, mother board) to beconnected to the back surface of the printed circuit board may beconnected to the terminals of the capacitor through the via holes formedin the connection layer and the through holes formed in the coresubstrate. That is, although the accommodation layer having a corematerial is hard to process, though holes are formed in theaccommodation layer so that the terminals of the capacitors are notdirectly connected to the outside surface. As a result, the reliabilityof the connection can be increased.

A wiring for connecting an IC chip and an external substrate may beprovided between capacitors, and a signal line does not pass through thechip capacitors. This structure eliminates the problems that theimpedance becomes discontinuous by the high dielectric body to generatea reflection, and that the transmission is delayed by passing throughthe high dielectric body. By mounting a capacitor for power supply,large electric power can be easily supplied to the IC chip. Furthermore,noise generated when a signal is transmitted in the printed circuitboard can be reduced.

In addition, by providing a wiring for connection, it becomes possibleto provide a wiring below the capacitors. In this manner, a wiring hasan increased degree of freedom, thereby attaining high density and smallsize.

A chip capacitor in which electrodes are formed along an inside of theouter edge thereof may be used. With this arrangement, a large space canbe used for external electrodes even if a conduction is establishedthrough the via holes, and therefore, the broadened range of alignmentis allowed. As a result, a problem of disconnection is eliminated.

A chip capacitor in which electrodes are formed in matrix may be used.It becomes easy to accommodate a large chip capacitor in a coresubstrate. Therefore, it becomes possible to increase an electrostaticcapacity, and a problem concerning electricity can be solved. Inaddition, warpage is hard to generate in the printed circuit board evenif the printed circuit board undergoes various thermal histories.

A plurality of chip capacitors from each of which a plurality of piecesare to be obtained may be coupled to each other into one piece unit andused. In this manner, an electrostatic capacity can be properly adjustedand the IC chip can be properly operated.

A capacitor may be mounted on the surface of the printed circuit boardon top of the capacitors accommodated in the substrate. Since thecapacitors are accommodated within the printed circuit board, thedistance between the IC chip and each capacitor is shortened. Inaddition, the loop inductance can be lowered, and electric power can beinstantaneously provided. On the other hand, since a capacitor isprovided on the surface of the printed circuit board as well, acapacitor having a large capacity can be mounted. In this manner, largeelectric power can be easily supplied to the IC chip.

The chip capacitor mounted on the surface of the printed circuit boardmay have an electrostatic capacity same or larger than the electrostaticcapacity of the chip capacitor incorporated in the printed circuitboard. In this manner, there is no shortage of power supply at a highfrequency domain, and the IC chip reliably exhibits a desired operation.

The chip capacitor mounted on the surface of the printed circuit boardmay have an inductance same or smaller than the inductance of the chipcapacitor incorporated in the printed circuit board. In this manner,there is no shortage of power supply at a high frequency domain, and theIC chip reliably exhibits a desired operation

The surface of the chip capacitor may be subjected to rougheningtreatment. The rough surface contributes to an increased adhesionbetween the chip capacitor made of ceramic and a connection layer and aresin insulating layer made of resin, thereby avoiding the connectionlayer and the interlayer resin insulating layer from peeling from theinterface with the chip capacitors even when a heat cycle test isconducted.

Copper may be provided around the respective chip capacitors. In thismanner, no migration is generated in the capacitors incorporated in theprinted circuit board. In addition, the capacitors never peel from theresin charged between the capacitors, and no cracks are created. Theaccommodation characteristic is enhanced, and as a result, there is nodeterioration in electric characteristics.

A resin may be charged between the spot-faced section of the coresubstrate and the capacitor. The thermal expansion coefficient of theresin is set to the value lower than the thermal expansion coefficientof the core substrate, that is, is set to the value close to that of thechip capacitor made of ceramics. In this manner, even if internal stressis generated between the core substrate and the resin insulating layer,and the chip capacitor caused by the difference in the thermal expansioncoefficients therebetween, cracks and peelings do not easily occur. As aresult, high reliability can be attained. In addition, the generation ofmigration can be prevented.

A method for manufacturing a printed circuit board is characterized bycomprising at least the following steps (a) to (c):

(a) forming a circuit pattern on a resin plate on its one side or bothsides, and connecting a capacitor to the circuit pattern through anadhesive material;

(b) attaching a resin substrate formed with a cavity for accommodatingthe capacitor to the resin plate to form a core substrate; and

(c) forming openings extending to electrodes of the capacitor in theresin plate to form via holes.

In the method for manufacturing a printed circuit board, it becomespossible to accommodate chip capacitors in a core substrate. As aresult, a printed circuit board having a lowered loop inductance can beprovided.

In the method for manufacturing a printed circuit board, a resinsubstrate accommodating capacitors and a resin plate may be attached toeach other by applying a pressure from both sides to form a coresubstrate. Thus-formed core substrate has a flat surface. As a result,an interlayer resin insulating layer and a conductor circuit having highreliability can be laminated on the core substrate.

In the method for manufacturing a printed circuit board, a through holefor an IC chip and an external substrate may be provided betweencapacitors. A signal line does not pass through the chip capacitors 20made of ceramics. This structure eliminates the problems that theimpedance becomes discontinuous by the high dielectric body to generatea reflection, and that the transmission is delayed by passing throughthe high dielectric body. By mounting a capacitor for power supply, itbecomes possible to easily provide large electric power to the IC chip.

In order to solve the above-described problems, a printed circuit boardincorporates a core substrate, and a resin insulating layer and aconductor circuit laminated to a core substrate. The core substrateincorporates a connection layer formed by an insulating resin layerincluding at least one or more layer, and an accommodation layer formedby a resin layer accommodating capacitors and including two or morelayers.

It means the circuit formed by buildup method where an interlayer resininsulating layer is formed on the core substrate, and via holes orthrough holes are formed in the interlayer resin insulating layer toform a conductor circuit as a conductive layer. As the buildup layer, asemi-additive method or a fully-additive method may be employed.

In the printed circuit board, capacitors are mounted within the printedcircuit board. In this manner, the distance between the IC chip and eachcapacitor is shortened, and the loop inductance can be lowered. The coresubstrate incorporates one or more connection layers and anaccommodation layer for accommodating the capacitors. Since thecapacitors are accommodated within the accommodation layer having largethickness, the thickness of the core substrate does not become thick.The thickness of the printed circuit board does not become thick even ifthe interlayer resin insulating layer and the conductor circuit arelaminated on the core substrate.

It is desirable to fill the cavity with a resin. As a result, thebehavior of the capacitors incorporated in the core substrate becomessmall. In addition, even if the stress is generated caused by thecapacitors, the stress can be alleviated by the resin. The resin alsohas an effect of adhering the capacitors to the core substrate, andlowering a migration between the capacitors and the core substrate.

A printed circuit board is characterized by comprising a resininsulating layer and a conductor circuit laminated to the coresubstrate,

wherein the core substrate incorporates a connection layer formed by aninsulating resin layer including at least one or more layer, and anaccommodation layer formed by a resin layer accommodating a capacitorand including two or more layers, and vias for establishing a connectionwith the capacitor are formed on both sides of the core substrate.

In the printed wiring board, capacitors are mounted within the printedcircuit board. In this manner, the distance between the IC chip and eachcapacitor is shortened, and the loop inductance can be lowered. The coresubstrate is constituted by at least one or more connection layer and anaccommodation layer for accommodating the capacitors. Since thecapacitors are accommodated within the accommodation layer having largethickness, the thickness of the core substrate does not become large.The thickness of the printed circuit board does not become large even ifthe interlayer resin insulating layer and the conductor circuit arelaminated on the core substrate. Furthermore, since vias to be connectedto the capacitors are formed on both sides, the wire length from thecapacitors to the IC chip and the external substrate is shortened.

A wiring for connecting an IC chip and an external substrate may beprovided between capacitors, and a signal line does not pass through thechip capacitors. This structure eliminates the problems that theimpedance becomes discontinuous by the high dielectric body to generatea reflection, and that the transmission is delayed by passing throughthe high dielectric body. By mounting a capacitor for power supply,large electric power can be easily supplied to the IC chip. Furthermore,by providing a capacitor for ground, noise generated when a signal istransmitted in the printed circuit board can be reduced.

In addition, by providing a wiring for connection, it becomes possibleto provide a wiring below the capacitors. In this manner, a wiring hasan increased degree of freedom, thereby attaining high density and smallsize.

A chip capacitor in which electrodes are formed along an inside of theouter edge thereof may be used. With this arrangement, a large space canbe used for external electrodes even if a conduction is establishedthrough the via holes, and therefore, the broadened range of alignmentis allowed. As a result, a problem of disconnection is eliminated.

A chip capacitor in which electrodes are formed in matrix may be used.It becomes easy to accommodate a large chip capacitor in a coresubstrate. Therefore, it becomes possible to increase an electrostaticcapacity, and a problem concerning electricity can be solved. Inaddition, warpage is hard to generate in the printed circuit board evenif the printed circuit board undergoes various thermal histories.

A plurality of chip capacitors from each of which a plurality of piecesare to be obtained may be coupled to each other into one piece unit andused. In this manner, an electrostatic capacity can be properly adjustedand the IC chip can be properly operated.

A capacitor may be mounted on the surface of the printed circuit boardon top of the capacitors accommodated in the substrate. Since thecapacitors are accommodated within the printed circuit board, thedistance between the IC chip and each capacitor is shortened. Inaddition, the loop inductance can be lowered, and electric power can beinstantaneously provided. On the other hand, since a capacitor isprovided on the surface of the printed circuit board as well, acapacitor having a large capacity can be mounted. In this manner, largeelectric power can be easily supplied to the IC chip.

The chip capacitor mounted on the surface of the printed circuit boardmay have an electrostatic capacity same or larger than the electrostaticcapacity of the chip capacitor incorporated in the printed circuitboard. In this manner, there is no shortage of power supply at a highfrequency domain, and the IC chip reliably exhibits a desired operation.

The chip capacitor mounted on the surface of the printed circuit boardmay have an inductance same or larger than the inductance of the chipcapacitor incorporated in the printed circuit board. In this manner,there is no shortage of power supply at a high frequency domain, and theIC chip reliably exhibits a desired operation.

An electric connection for electrodes formed with a metal film of thecapacitors may be established by via holes formed by plating. Theelectrodes of the chip capacitor are made by metallizing, and have pitsand projections on their surfaces. However, the surfaces become smoothby formation of the metal film, and the via holes are then formed on thesmooth surfaces. In this manner, when penetrating openings are formed inthe resin coating the electrodes, no resin remains, and a reliability ofthe connection between the via holes and the electrodes can beincreased. Furthermore, since the via holes are made by plating into theelectrodes formed with the copper plated film, the electrodes are firmlyconnected to the via holes. No disconnection occurs between theelectrodes and via holes even when a heat cycle test is conducted.

The metal film formed on the electrodes of the capacitors preferablyincludes any one of metals selected from the group consisting of copper,nickel, and noble metals. Tins and zinc are not preferable, because ifthe capacitors incorporated in the printed circuit board have a filmincluding these metals formed on their electrodes, a migration is easilygenerated at a connection with the via holes.

The surfaces of the chip capacitors may be roughened. The rough surfacecontributes to an increased adhesion between the chip capacitor made ofceramic, and a connection layer and a resin insulating layer made ofresin, thereby avoiding the resin insulating layer from peeling from theinterface with the chip capacitor even when a heat cycle test isconducted.

The chip capacitors may be accommodated in the printed circuit board inthe state where at least a part of the electrodes of each capacitor isuncoated with a coating layer and exposed to the outside. An electricconnection for the electrode exposed from the coating layer isestablished. The metal exposed from the coating layer preferablyincludes copper as a main component, because the connection resistancecan be lowered.

The thermal expansion coefficient of the insulating adhesive may be setto the value lower than the thermal expansion coefficient of theaccommodating layer, that is, is set to the value close to that of thechip capacitor made of ceramics. In this manner, even if internal stressis generated between the core substrate and the resin insulating layer,and the chip capacitor caused by the difference in the thermal expansioncoefficients therebetween, cracks and peelings do not easily occur whena heat cycle test is conducted. As a result, high reliability can beattained.

A method for manufacturing a printed circuit board is characterized bycomprising at least the following steps (a) to (e):

(a) forming penetrating openings for accommodating a capacitor in afirst resin material having a core material impregnated with a resin;

(b) attaching a second resin material to the first resin material formedwith the penetrating openings to form an accommodation layer having asection for accommodating a capacitor;

(c) accommodating the capacitor in the accommodation layer;

(d) attaching a third insulating resin layer to the accommodation layerformed in the step (c) to form a core substrate; and

(e) forming openings extending to electrodes of the capacitor in thethird insulating resin layer to form via holes.

A method for manufacturing a printed circuit board is characterized bycomprising at least the following steps (a) to (e):

(a) forming penetrating openings for accommodating a capacitor in afirst resin material having a core material impregnated with a resin;

(b) providing a capacitor to the second resin material at a positioncorresponding to a section for accommodating a capacitor in the resinmaterial;

(c) attaching the first resin material subjected to the step (a) and thesecond resin material subjected to the step (b) to each other to form anaccommodation layer accommodating the capacitor;

(d) attaching a third insulating resin layer to the accommodation layerto form a core substrate; and

(e) forming openings in the third insulating resin layer extending toelectrodes of the capacitor to form via holes.

A method for manufacturing a printed circuit board is characterized bycomprising at least the following steps (a) to (f):

(a) forming penetrating openings for accommodating a capacitor in afirst resin material having a core material impregnated with a resin;

(b) providing a capacitor to the second resin material at a positioncorresponding to a section for accommodating a capacitor in the resinmaterial;

(c) attaching the first resin material subjected to the step (a) and thesecond resin material subjected to the step (b) to each other to form anaccommodation layer accommodating the capacitor;

(d) attaching a third insulating resin layer to the accommodation layerto form a core substrate;

(e) forming openings in the third insulating resin layer extending toelectrodes of the capacitor to form via holes; and

(f) forming a conductive film in the penetrating openings of the firstresin material and the openings of the third resin material to form viaholes.

In the method for manufacturing a printed circuit board, it becomespossible to accommodate chip capacitors in a core substrate. As aresult, a printed circuit board having a lowered loop inductance can beprovided.

In the method for manufacturing a printed circuit board, it becomespossible to accommodate chip capacitors in a core substrate. As aresult, a printed circuit board having a lowered loop inductance can beprovided. Since via holes are formed on both surfaces of the coresubstrate, the wire length from the capacitors to the IC chip and theexternal substrate is shortened.

In the method for manufacturing a printed circuit board, a resinsubstrate accommodating capacitors and a resin plate may be attached toeach other by applying a pressure from both sides to form a coresubstrate. Thus-formed core substrate has a flat surface. As a result,an interlayer resin insulating layer and a conductor circuit having highreliability can be laminated on the core substrate.

A printed circuit board is characterized by comprising a core substrate,and a resin insulating layer and a conductor circuit laminated to thecore substrate,

wherein the core substrate incorporates an accommodating layer havingpenetrating openings in each of which a capacitor is accommodated, andconnection layers each made of an insulating resin layer and provided onthe front surface and the back surface of the accommodation layer.

It means the circuit formed by buildup method where an interlayer resininsulating layer is formed on the core substrate, and via holes orthrough holes are formed in the interlayer resin insulating layer toform a conductor circuit as a conductive layer. As the buildup layer, asemi-additive method or a fully-additive method may be employed.

Capacitors may be mounted within the printed circuit board. In thismanner, the distance between the IC chip and each capacitor isshortened, and the loop inductance can be lowered. The core substrateincorporates at least one or more connection layers and an accommodationlayer for accommodating the capacitors. Since the capacitors areaccommodated within the accommodation layer having large thickness, thethickness of the core substrate does not become large. The thickness ofthe printed circuit board does not become large even if the interlayerresin insulating layer and the conductor circuit are laminated on thecore substrate.

Since via holes are formed on both surfaces of the core substrate, thepower supply located on the substrate connected to the outside and thecapacitors accommodated in the substrate can be connected to each otherin a shortest distance. With this arrangement, a voltage can beinstantaneously supplied from the power supply to the IC chip, and thevoltage for driving the IC can be promptly stabilized.

The cavity is preferably filled with a resin. The resin eliminates aspace between the capacitors and the core substrate. As a result, thebehavior of the capacitors incorporated in the core substrate becomessmall. In addition, even if the stress is generated caused by thecapacitors, the stress can be alleviated by the resin. The resin alsohas an effect of adhering the capacitors to the core substrate, andlowering a migration between the capacitors and the core substrate.

An accommodation layer may be constituted by a resin substrate having acore material impregnated with a resin. As a result, sufficiently highstrength can be given to the core substrate.

The capacitors are fixed in the penetrating openings of theaccommodation layer through an insulating adhesive. In this manner, thecapacitors can be fixed to proper positions.

The IC chip mounted on the front surface of the printed circuit board,the external substrate mounted on the back surface of the printedcircuit board (i.e. daughter board, mother board) are connected to theterminals of the capacitors through the via holes formed in theconnection layer. That is, the terminals of the capacitors, the IC chip,and the external substrate are directly connected to each other. As aresult, the length of electric wire can be shortened.

A wiring for connecting an IC chip and an external substrate may beprovided between capacitors, and a signal line does not pass through thechip capacitors. This structure eliminates the problems that theimpedance becomes discontinuous by the high dielectric body to generatea reflection, and that the transmission is delayed by passing throughthe high dielectric body. By mounting a capacitor for power supply,large electric power can be easily supplied to the IC chip. Furthermore,by providing a capacitor for ground, noise generated when a signal istransmitted in the printed circuit board can be reduced. In addition, byproviding a wiring for connection, it becomes possible to provide awiring below the capacitors. In this manner, a wiring has an increaseddegree of freedom, thereby attaining high density and small size.

A capacitor may be mounted on the surface of the printed circuit boardon top of the capacitors accommodated in the substrate. Since thecapacitors are accommodated within the printed circuit board, thedistance between the IC chip and each capacitor is shortened. Inaddition, the loop inductance can be lowered, and electric power can beinstantaneously provided. On the other hand, since a capacitor isprovided on the surface of the printed circuit board as well, acapacitor having a large capacity can be mounted. In this manner, largeelectric power can be easily supplied to the IC chip.

The chip capacitor mounted on the surface of the printed circuit boardmay have an electrostatic capacity same or larger than the electrostaticcapacity of the chip capacitor incorporated in the printed circuitboard. In this manner, there is no shortage of power supply at a highfrequency domain, and the IC chip reliably exhibits a desired operation.

The chip capacitor mounted on the surface of the printed circuit boardmay have an inductance same or larger than the inductance of the chipcapacitor incorporated in the printed circuit board. In this manner,there is no shortage of power supply at a high frequency domain, and theIC chip reliably exhibits a desired operation

A chip capacitor in which electrodes are formed along an inside of theouter edge thereof may be used. With this arrangement, a large space canbe used for external electrodes even if a conduction is establishedthrough the via holes, and therefore, the broadened range of alignmentis allowed. As a result, a problem of disconnection is eliminated.

A chip capacitor in which electrodes are formed in matrix may be used.It becomes easy to accommodate a large chip capacitor in a coresubstrate. Therefore, it becomes possible to increase an electrostaticcapacity, and a problem concerning electricity can be solved. Inaddition, warpage is hard to generate in the printed circuit board evenif the printed circuit board undergoes various thermal history.

A plurality of chip capacitors which are coupled to each other into onepiece unit and from each of which a plurality of pieces are to beobtained may be used. In this manner, an electrostatic capacity can beproperly adjusted and the IC chip can be properly operated.

An electric connection for electrodes formed with a metal film of thecapacitors may be established by via holes formed by plating. Theelectrodes of the chip capacitor are made by metallizing, and have pitsand projections on their surfaces. However, the surfaces become smoothby formation of the metal film, and the via holes are then formed on thesmooth surfaces. In this manner, when penetrating openings are formed inthe resin coating the electrodes, no resin remains, and a reliability ofthe connection between the via holes and the electrodes can beincreased. Furthermore, since the via holes are made by plating into theelectrodes formed with the copper plated film, the electrodes are firmlyconnected to the via holes. No disconnection occurs between theelectrodes and via holes even when a heat cycle test is conducted.

The metal film formed on the electrodes of the capacitors preferablyincludes any one of metals selected from the group consisting of copper,nickel, and noble metals. Tins and zinc are not preferable, because ifthe capacitors incorporated in the printed circuit board has a filmincluding these metals formed on their electrodes, a migration is easilygenerated at a connection with the via holes.

The surfaces of the chip capacitors may be roughened. The rough surfacecontributes to an increased adhesion between the chip capacitor made ofceramic and a resin insulating layer made of resin, thereby avoiding theresin insulating layer from peeling from the interface with the chipcapacitor even when a heat cycle test is conducted.

The chip capacitors may be accommodated in the printed circuit board inthe state where at least a part of the electrodes of each capacitor isuncoated with a coating layer and exposed to the outside. An electricconnection for the electrode exposed from the coating layer isestablished. The metal exposed from the coating layer preferablyincludes copper as a main component, because the connection resistancecan be lowered.

The thermal expansion coefficient of the resin may be set to the valuelower than the thermal expansion coefficient of the core substrate, thatis, is set to the value close to that of the chip capacitor made ofceramics. In this manner, even if internal stress is generated betweenthe core substrate and the resin insulating layer, and the chipcapacitor caused by the difference in the thermal expansion coefficientstherebetween, cracks and peelings do not easily occur when a heat cycletest is conducted. As a result, high reliability can be attained. Inaddition, the generation of migration can be prevented.

A method for manufacturing a printed circuit board is characterized bycomprising at least the following steps (a) to (d):

(a) forming penetrating openings for accommodating a capacitor in afirst resin material having a core material impregnated with a resin;

(b) accommodating a capacitor in each of the penetrating openings of thefirst resin material;

(c) attaching a second resin material to the first resin material toform a core substrate; and

(d) forming openings extending to electrodes of the capacitor in thesecond resin material of the core substrate to form via holes.

In the method for manufacturing a printed circuit board, it becomespossible to accommodate chip capacitors in a core substrate. As aresult, a printed circuit board having a lowered loop inductance can beprovided.

A wiring for connecting an IC chip and an external substrate may beprovided between capacitors, and a signal line does not pass through thechip capacitors. This structure eliminates the problems that theimpedance becomes discontinuous by the high dielectric body to generatea reflection, and that the transmission is delayed by passing throughthe high dielectric body. By mounting a capacitor for power supply,large electric power can be easily supplied to the IC chip.

In the method for manufacturing a printed circuit board, a resinsubstrate accommodating capacitors and a resin plate are attached toeach other by applying a pressure from both sides to form a coresubstrate. Thus-formed core substrate has a flat surface. As a result,an interlayer resin insulating layer and a conductor circuit having highreliability can be laminated on the core substrate.

In order to solve the above-described problems, a printed circuit boardincorporates a core substrate, and a resin insulating layer and aconductor circuit laminated to a core substrate. The capacitors areaccommodated in the core substrate.

It means the circuit formed by buildup method where an interlayer resininsulating layer is formed on the core substrate, and via holes orthrough holes are formed in the interlayer resin insulating layer toform a conductor circuit as a conductive layer. As the buildup layer, asemi-additive method or a fully-additive method may be employed.

Capacitors may be mounted within the printed circuit board. In thismanner, the distance between the IC chip and each capacitor isshortened, and the loop inductance can be lowered. Since the capacitorsare accommodated within the accommodation layer having large thickness,the thickness of the core substrate does not become thick. The thicknessof the printed circuit board does not become thick even if theinterlayer resin insulating layer and the conductor circuit arelaminated on the core substrate.

It is desirable to fill the cavity with a resin. As a result, thebehavior of the capacitors incorporated in the core substrate becomessmall. In addition, even if the stress is generated caused by thecapacitors, the stress can be alleviated by the resin. The resin alsohas an effect of adhering the capacitors to the core substrate, andlowering a migration between the capacitors and the core substrate.

A printed circuit board is characterized by comprising a core substrate,and a resin insulating layer and a conductor circuit laminated to thecore substrate,

wherein the chip capacitor is accommodated in the printed circuit boardin the state where at least a part of electrodes of each capacitor isuncoated with a coating layer and exposed to the outside, and anelectric connection for the electrode exposed from the coating layer isestablished by plating.

The chip capacitors may be accommodated in the printed circuit board inthe state where at least a part of the electrodes of each capacitor isuncoated with a coating layer and exposed to the outside. An electricconnection for the electrode exposed from the coating layer isestablished. The metal exposed from the coating layer includespreferably copper as a main component. This is because the connection tothe exposed metal provided with plating is increased, and as a result,the difference in electric characteristics is cancelled and theconnection resistance can be lowered.

A printed circuit board is characterized by comprising a core substrate,and a resin insulating layer and a conductor circuit laminated to thecore substrate,

wherein the chip capacitor is accommodated in the state where a metalfilm is formed on electrodes of the capacitor, and an electricconnection for the electrodes formed with the metal film is establishedby plating.

An electric connection for electrodes formed with a metal film of thecapacitors may be established by via holes formed by plating. Theelectrodes of the chip capacitor are made by metallizing, and have pitsand projections on their surfaces. However, the surfaces become smoothby formation of the metal film, and the via holes are then formed on thesmooth surfaces. In this manner, when penetrating openings are formed inthe resin coating the electrodes, no resin remains, and a reliability ofthe connection between the via holes and the electrodes can beincreased. Furthermore, since the via holes are made by plating into theelectrodes formed with the copper plated film, the electrodes are firmlyconnected to the via holes. No disconnection occurs between theelectrodes and via holes even when a heat cycle test is conducted.

The metal film formed on the electrodes of the capacitors preferablyincludes any one of metals selected from the group consisting of copper,nickel, and noble metals. Tins and zinc are not preferable, because ifthe capacitors incorporated in the printed circuit board has a filmincluding these metals formed on their electrodes, a migration is easilygenerated at a connection with the via holes. Since tins and zinc arenot used in the present invention, the generation of migration can beprevented.

A chip capacitor in which electrodes are formed along an inside of theouter edge thereof may be used. With this arrangement, a large space canbe used for external electrodes even if a conduction is establishedthrough the via holes, and therefore, the broadened range of alignmentis allowed. As a result, a problem of disconnection is eliminated.

A chip capacitor in which electrodes are formed in matrix may be used.It becomes easy to accommodate a large chip capacitor in a coresubstrate. In addition, warpage is hard to generate in the printedcircuit board even if the printed circuit board undergoes variousthermal histories.

A plurality of chip capacitors from each of which a plurality of piecesare to be obtained may be coupled to each other into one piece unit andused. In this manner, an electrostatic capacity can be properly adjustedand the IC chip can be properly operated.

A printed circuit board is characterized by comprising a core substrate,and a resin insulating layer and a conductor circuit laminated to thecore substrate,

wherein a capacitor is accommodated in the core substrate, and acapacitor is mounted on the surface of the printed circuit board.

A capacitor may be mounted on the surface of the printed circuit boardon top of the capacitors accommodated in the substrate. Since thecapacitors are accommodated within the printed circuit board, thedistance between the IC chip and each capacitor is shortened. Inaddition, the loop inductance can be lowered, and electric power can beinstantaneously provided. On the other hand, since a capacitor isprovided on the surface of the printed circuit board as well, acapacitor having a large capacity can be mounted. In this manner, largeelectric power can be easily supplied to the IC chip.

The chip capacitor mounted on the surface of the printed circuit boardmay have an electrostatic capacity same or larger than the electrostaticcapacity of the chip capacitor incorporated in the printed circuitboard. In this manner, there is no shortage of power supply at a highfrequency domain, and the IC chip reliably exhibits a desired operation.

The chip capacitor mounted on the surface of the printed circuit boardmay have an inductance same or larger than the inductance of the chipcapacitor incorporated in the printed circuit board. In this manner,there is no shortage of power supply at a high frequency domain, and theIC chip reliably exhibits a desired operation

The surface of the chip capacitor may be subjected to rougheningtreatment. The rough surface contributes to an increased adhesionbetween the chip capacitor made of ceramic, and a connection layer and aresin insulating layer made of resin, thereby avoiding the connectionlayer and the interlayer resin insulating layer from peeling from theinterface with the chip capacitor even when a heat cycle test isconducted.

A copper plated film may be coated on the surface of a metallizedelectrodes of a chip capacitor.

A metal film may be formed on the electrodes of the chip capacitors. Asa result, the chip capacitor have a flat surface. When the chipcapacitors are accommodated in the printed circuit board, andpenetrating openings are formed in the resin which covers theelectrodes, no resin is left. In this manner, the connection between thevia holes and the electrodes has increased reliability.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a diagram showing a process for manufacturing a printedcircuit board according to a first embodiment of the present invention.

FIG. 2 is a diagram showing a process for manufacturing a printedcircuit board according to a first embodiment.

FIG. 3 is a diagram showing a process for manufacturing a printedcircuit board according to a first embodiment.

FIG. 4 is a diagram showing a process for manufacturing a printedcircuit board according to a first embodiment.

FIG. 5 is a diagram showing a process for manufacturing a printedcircuit board according to a first embodiment.

FIG. 6 is a diagram showing a process for manufacturing a printedcircuit board according to a first embodiment.

FIG. 7 is a diagram showing a cross section of the printed circuit boardaccording to a first embodiment.

FIG. 8 is a diagram showing a cross section of the state where an ICchip is mounted on the printed circuit board according to the firstembodiment.

FIG. 9 is a diagram showing a process for manufacturing a printedcircuit board according to a first modification of the first embodiment.

FIG. 10 is a diagram showing a process for manufacturing a printedcircuit board according to a first modification of the first embodiment.

FIG. 11 is a diagram showing a process for manufacturing a printedcircuit board according to a first modification of the first embodiment.

FIG. 12 is a diagram showing a process for manufacturing a printedcircuit board according to a first modification of the first embodiment.

FIG. 13 is a diagram showing a process for manufacturing a printedcircuit board according to a first modification of the first embodiment.

FIG. 14 is a diagram showing a process for manufacturing a printedcircuit board according to a first modification of the first embodiment.

FIG. 15 is a diagram showing a cross section of the state where an ICchip is mounted on the printed circuit board according to the firstmodification of the first embodiment.

FIG. 16 is a diagram showing a process for manufacturing a printedcircuit board according to a second modification of the firstembodiment.

FIG. 17 is a diagram showing a cross section of the chip capacitoraccording to the first embodiment.

FIG. 18 is a plan view showing a chip capacitor according to a thirdmodification of the first embodiment.

FIG. 19 is a plan view showing a chip capacitor according to a thirdmodification of the first embodiment.

FIG. 20 is a plan view showing a chip capacitor according to a thirdmodification of the first embodiment.

FIG. 21 is a diagram showing a cross section of the printed circuitboard according to a fourth modification of the first embodiment.

FIG. 22 is a graph showing the changes in the voltage supplied to the ICchip and the time.

FIG. 23 is a diagram showing a process for manufacturing a printedcircuit board according to a second embodiment of the present invention.

FIG. 24 is a diagram showing a process for manufacturing a printedcircuit board according to a second embodiment.

FIG. 25 is a diagram showing a process for manufacturing a printedcircuit board according to a second embodiment.

FIG. 26 is a diagram showing a process for manufacturing a printedcircuit board according to a second embodiment.

FIG. 27 is a diagram showing a process for manufacturing a printedcircuit board according to a second embodiment.

FIG. 28 is a diagram showing a process for manufacturing a printedcircuit board according to a second embodiment.

FIG. 29 is a diagram showing a cross section of the printed circuitboard according to a second embodiment.

FIG. 30 is a diagram showing a cross section of the printed circuitboard according to a second embodiment.

FIG. 31 is a diagram showing a cross section of the printed circuitboard according to a first modification of the second embodiment.

FIG. 32 is a diagram showing a cross section of the printed circuitboard according to a second modification of the second embodiment.

FIG. 33 is a diagram showing a cross section of the printed circuitboard according to a third modification of the second embodiment.

FIG. 34 is a diagram showing a process for manufacturing a printedcircuit board according to a third embodiment of the present invention.

FIG. 35 is a diagram showing a process for manufacturing a printedcircuit board according to a third embodiment.

FIG. 36 is a diagram showing a process for manufacturing a printedcircuit board according to a third embodiment.

FIG. 37 is a diagram showing a cross section of the printed circuitboard according to a third embodiment.

FIG. 38 is a diagram showing a cross section of the printed circuitboard according to a third embodiment.

FIG. 39 is a diagram showing a cross section of the printed circuitboard according to a first modification of the third embodiment.

FIG. 40 is a diagram showing a process for manufacturing a printedcircuit board according to a second modification of the thirdembodiment.

FIG. 41 is a diagram showing a process for manufacturing a printedcircuit board according to a second modification of the thirdembodiment.

FIG. 42 is a diagram showing a cross section of the printed circuitboard according to a second modification of the third embodiment.

FIG. 43 is a diagram showing a process for manufacturing a printedcircuit board according to third modification of the third embodiment.

FIG. 44 is a diagram showing a cross section of the printed circuitboard according to a third modification of the third embodiment.

FIG. 45 is a diagram showing a cross section of the chip capacitor.

FIG. 46 is a diagram showing a cross section according to a fourthmodification of the third embodiment.

FIG. 47 is a diagram showing a cross section of the chip capacitoraccording to the fourth modification.

FIG. 48 is a diagram showing a process for manufacturing a printedcircuit board according to a fourth embodiment of the present invention.

FIG. 49 is a diagram showing a process for manufacturing a printedcircuit board according to a fourth embodiment.

FIG. 50 is a diagram showing a process for manufacturing a printedcircuit board according to a fourth embodiment.

FIG. 51 is a diagram showing a cross section of the printed circuitboard according to a fourth embodiment.

FIG. 52 is a diagram showing a cross section of the printed circuitboard according to a fourth embodiment.

FIG. 53 is a diagram showing a cross section of the printed circuitboard according to a first modification of the fourth embodiment.

FIG. 54 is a diagram showing a cross section of the printed circuitboard according to a second modification of the fourth embodiment.

FIG. 55 is a diagram showing a cross section of the printed circuitboard according to a third modification of the fourth embodiment.

FIG. 56 is a diagram showing a cross section of the printed circuitboard according to a fourth modification of the fourth embodiment.

FIG. 57 is a diagram showing a cross section of the printed circuitboard according to a fifth modification of the fourth embodiment.

FIG. 58 is a diagram showing a cross section of the printed circuitboard according to a sixth modification of the fourth embodiment.

FIG. 59 is a diagram showing a cross section of the chip capacitoraccording to the sixth modification.

FIG. 60 is a diagram showing a process for manufacturing a printedcircuit board according to a fifth embodiment of the present invention.

FIG. 61 is a diagram showing a process for manufacturing a printedcircuit board according to a fifth embodiment.

FIG. 62 is a diagram showing a process for manufacturing a printedcircuit board according to a fifth embodiment.

FIG. 63 is a diagram showing a cross section of the printed circuitboard according to a fifth embodiment.

FIG. 64 is a diagram showing a cross section of the printed circuitboard according to a fifth embodiment.

FIG. 65 is a diagram showing a cross section of the printed circuitboard according to a first modification of the fifth embodiment.

FIG. 66 is a diagram showing a cross section of the chip capacitoraccording to the first modification.

FIG. 67 is a diagram showing a cross section of the printed circuitboard according to a second modification of the fifth embodiment.

FIG. 68 is a diagram showing a cross section of the chip capacitoraccording to the second modification.

FIG. 69 is a diagram showing a cross section of the printed circuitboard according to a third modification of the fifth embodiment.

FIG. 70 is a diagram showing a cross section of the printed circuitboard according to a fourth modification of the present invention.

FIG. 71 is a diagram showing a cross section of the printed circuitboard according to a fifth modification.

FIG. 72 is a diagram showing a cross section according to a sixthmodification.

FIG. 73 is a diagram illustrating a loop inductance of a printed circuitboard according to a conventional technique.

BEST MODE FOR CARRYING OUT THE INVENTION First Embodiment

Hereinafter, embodiments of the present invention will be described withreference to the drawings.

First, the structure of a printed circuit board according to a firstembodiment of the present invention will be described with reference toFIGS. 7 and 8. FIG. 7 is a diagram showing a cross section of a printedcircuit board 10. FIG. 8 is a diagram showing a state where an IC chip90 is mounted on the printed circuit board 10 shown in FIG. 7, and theprinted circuit board 10 is attached onto a daughter board 95.

As shown in FIG. 7, the printed circuit board 10 is constituted by acore substrate 30 accommodating a plurality of chip capacitors 20, and abuildup circuit layers 80A, 80B. The buildup circuit layers 80A and 80Bare constituted by an interlayer resin insulating layer 50 and 150. Theinterlayer resin insulating layer 50 has via holes 160 and conductorcircuits 158. The interlayer resin insulating layer 150 has via holes161 and conductor circuits 159. A solder resist layer 70 is formed onthe interlayer resin insulating layer 150.

As shown in FIG. 17(A), the chip capacitor 20 is constituted by a firstelectrode 21, a second electrode 22, and a dielectric body 23 interposedbetween the first and second electrodes 21, 22. The dielectric body 23includes a plurality of first conductive films 24 connected to the firstelectrode 21 and a plurality of second conductive films 25 connected tothe second electrode 22 in an opposed relation to each other.

As shown in FIG. 8, a solder bump 76U is formed in each via hole 161 onthe upper buildup circuit layer 80A to connect the buildup circuit layer80A to each pad 92 of the IC chip 90. On the other hand, a solder bump76D is formed in each via hole 161 on the lower buildup circuit layer80B to connect the lower buildup circuit layer 80B to each pad 94 of thedaughter board 95. Through holes 46 are formed in the core substrate 30.

In this embodiment, the printed circuit board 10 is formed with a largecavity 32. Due to this structure, a plurality of chip capacitors 20 canreliably be arranged on the substrate even if the accuracy ofspot-facing process is low. The chip capacitors 20 can be arranged inpositions close to each other in the cavity 32, thereby increasing thepackaging density of the capacitors. In addition, the plurality of chipcapacitors 20 are arranged at identical heights to each other in thecavity 32, and therefore, as will be described later, the resin layercan be formed on the core substrate into a uniform thickness, and thevia holes can be stably formed. Since the interlayer resin insulatinglayers 50, 150, and the conductor circuits 158, 159 can be appropriatelyformed on the core substrate 30, the rate of generating defectiveprinted circuit boards 10 can be lowered.

As the material of the core substrate, a resin material is used. Forexample, resin materials used for general printed circuit boards, suchas base materials impregnated with glass epoxy resin and base materialsimpregnated with phenolic resin. It is impossible to use substrates madeof ceramic and AIN as the core substrate. These substrates are poor inouter shape processing characteristics, and cannot accommodatecapacitors in some cases. In addition, a void is created inside thesubstrate even if it is filled with a resin.

Since a resin layer 36 is charged into the space between the chipcapacitors 20, the chip capacitors 20 can be located and firmly fixed ataccurate positions in the cavity 32. In addition, the migration at theconnection between the capacitors and the via holes can be prevented.

The thermal expansion coefficients of the resin layer 36 and theadhesive material 34 provided on the bottom surface of the chipcapacitor 20 are set to the values lower than those of the coresubstrate 30 and the resin insulating layer 40, that is, are set to thevalues close to that of the chip capacitor 20 made of ceramics. In thismanner, even if internal stress is generated between the core substrate30 and the resin insulating layer 40, and the chip capacitors 20 causedby the difference in the thermal expansion coefficients therebetween,cracks and peelings on the core substrate 30 and the resin insulatinglayer 40 do not easily occur. As a result, high reliability can beattained.

Since the resin layer 36 provided between the chip capacitors 20 has thethrough holes 46, a signal line does not pass through the chipcapacitors 20 made of ceramics. This structure eliminates the problemsthat the impedance becomes discontinuous by the high dielectric body togenerate a reflection, and that the transmission is delayed by passingthrough the high dielectric body. It is possible to provide wires underthe capacitors, and external terminals such as wires and pins have anincreased degree of freedom, thereby attaining high density and smallsize.

As shown in FIG. 17(A), in the chip capacitor 20, the first electrode 21and second electrode 22 respectively include a metal layer 26 and acopper plated film 29 coating the metal layer 26. The plated film isformed by electrolytic plating, electroless plating, and the like. Asshown in FIG. 7, an electric connection for the first and secondelectrodes 21, 22 coated with the copper plated film 29 is establishedby the via hole 60 made of copper plating. The electrodes 21, 22 of thechip capacitor are metallized and has pits and projections on theirsurfaces. If the metal layer 26 is left uncoated and exposed to theoutside, the resin may be left in the pits and projections in the stepof forming openings 48 in the resin insulating layer 40 which will bedescribed later. The resin left in the pits and projections may cause adisconnection between the first and second electrodes 21, 22 and the viahole 60. Contrary to this, in the embodiment of the present invention,the surfaces of the first and second electrodes 21, 22 coated with thecopper plated film 29 are flat and smooth. When the openings 48 areformed in the resin insulating layer 40 formed on the electrodes 21, 22,no resin is left on the surfaces of the electrodes 21, 22. When the viaholes 60 are formed, the connection between the via holes 60 and theelectrodes 21, 22 has increased reliability.

Since the via holes 60 are made by plating into the electrodes 21, 22formed with the copper plated film 29, the electrodes 21, 22 are firmlyconnected to the via holes 60. No disconnection occurs between theelectrodes 21, 22 and via holes 60 even when a heat cycle test isconducted.

The copper plated film 29 is formed after a nickel/tin layer providedonto the surface of the metal layer 26 in the step of manufacturing thechip capacitor is peeled off at the time of mounting the chip capacitoronto the printed circuit board. Alternatively, the copper plated film 29may be directly provided onto the surface of the metal layer 26 in thestep of manufacturing the chip capacitor 20. In this embodiment,openings which extend to the copper plated film 29 of the electrodes isformed by a laser, and then a desmear process is performed to form viaholes by copper plating. Therefore, even if an oxide film is formed onthe surface of the copper plated film 29, the oxide film can be removedin the laser or desmear process. In this manner, the first and secondelectrodes 21, 22 can be properly connected to the via holes 60.

As shown in FIG. 17(B), the first and second electrodes 21, 22 of thecapacitor 20 may be partially uncoated with the coating 28. Whenpartially uncoated and exposed to the outside, the connection of thefirst and second electrodes 21, 22 to the via holes 60 can be enhanced.

On the surface of the dielectric body 23 made of ceramic of the chipcapacitor 20, a rough surface 23 α may be formed. The rough surface 23αcontributes to an increased adhesion between the chip capacitor 20 madeof ceramic and a resin insulating layer 40 made of resin, therebyavoiding the resin insulating layer 40 from peeling from the interfacewith the chip capacitor 20 even when a heat cycle test is conducted. Therough surface 23α can be formed by polishing the surface of the chipcapacitor 20 after the sintering step, or by roughening the surface ofthe chip capacitor 20 before the sintering step. In this embodiment, thesurface of the chip capacitor is roughened to increase its adhesion withthe resin insulating layer. Alternatively, the surface of the chipcapacitor may be subjected to silane coupling process.

Next, the method for manufacturing the printed circuit board, describedabove with reference to FIG. 7, will be described with reference toFIGS. 1 to 7.

(1) First, a core substrate 30 which is an insulating resin substrate isused as a starting material (FIG. 1(A)). Then, a cavity 32 foraccommodating capacitors is formed on one side of the core substrate 30by a spot-facing process (FIG. 1(B)). At this time, the cavity 32 isformed to have an area larger than the area in which a plurality ofcapacitors are to be provided. In this manner, a plurality of capacitorscan be provided on the core substrate 30 assuredly.

(2) After that, an adhesive material 34 is applied onto the cavity 32 bya printer (FIG. 1(C)). At this time, potting may be conducted on top ofthe application of the adhesive material 34. As the adhesive material34, an adhesive material having a thermal expansion coefficient smallerthan those of the core substrate 30 and the resin insulating layer 40 isused. Then, a plurality of chip capacitors 20 (FIG. 17) made of ceramicare placed onto the adhesive material 34 (FIG. 1(D)). By placing aplurality of chip capacitors 20 onto the cavity 32 having a flat andsmooth bottom surface, the plurality of chip capacitor 20 are alignedinto the same heights with each other. Thus-obtained core substrate 30has a flat and smooth surface. In addition, since the cavity 32 has alarge area, the chip capacitors 20 can be located at accurate positionswith high density.

(3) The top surfaces of the chip capacitors 20 are pushed or tapped toalign the chip capacitors 20 into the same heights with each other (FIG.2(A)). By this process, even if chip capacitors 20 having largelydifferent sizes from each other are provided in the cavity 32, they arealigned into the completely same heights with each other. As a result,the core substrate 30 can has a flat and smooth surface.

(4) After that, a thermosetting resin is charged into the space betweenthe chip capacitors 20 in the cavity 32, and then is heated and cured toform a resin layer 36 (FIG. 2(B)). The thermosetting resin is preferablyselected from the group consisting of epoxy, phenol, polyimide, andtriazine. The resin layer 36 serves to fix the chip capacitors 20 in thecavity 32. For the resin layer 36, a resin having a thermal expansioncoefficient smaller than those of the core substrate 30 and the resininsulating layer 40 is used.

Alternatively, the resin layer 36 may be made of other resins such asthermoplastic resin. The resin may be impregnated with a filler foradjusting the thermal expansion coefficient. Examples of the fillerinclude inorganic fillers, ceramic fillers, and metal fillers.

(5) Onto thus-obtained structure, a resin selected from epoxy resinswhich will be described later is applied with a printer to form a resininsulating layer 40 (FIG. 2(C)). Instead of applying the resin, a resinfilm may be attached.

Instead of epoxy resins, it is also possible to use one or more resinsselected from the group consisting of thermosetting resins,thermoplastic resins, photosensitive resins, complexes of thermosettingresins and thermoplastic resins, and complexes of photosensitive resinsand thermoplastic resins. The resin insulating layer may havetwo-layered structure made of these resins.

(6) After that, openings 48 for via holes are formed in the resininsulating layer 40 by a laser (FIG. 2(D)), and then, a desmear processis conducted. Instead of the process using a laser, exposure to lightand development may be employed. Then, penetrating openings 46 a forthrough holes are formed with a drill or laser, and are heated and cured(FIG. 3(A)). Alternatively, a desmear process using a drug solution ofpermagnetic acid or plasma may be conducted.

(7) A copper plated film 52 is formed on the surface of the resininsulating layer 40 by an electroless copper plating (FIG. 3(B)).Instead of the electroless plating to form the copper plated film 52, itis also possible to conduct sputtering using an Ni—Cu alloy as a targetto form an Ni—Cu alloy layer. As the case may be, after the sputteringto form the Ni—Cu alloy layer, an electroless plated film may be formedthereon.

(8) A photosensitive dry film is attached on the surface of the copperplated film 52, and a mask is placed thereon. In this state, exposure tolight and development are conducted to form a resist 54 having apredetermined pattern. The resultant core substrate 30 is immersed intoan electrolytic plating solution, and a current is allowed to flow intothe core substrate 30 through the copper plated film 52 to precipitatean electrolytic plated film 56 (FIG. 3(C)).

(9) The plated resist 54 is peeled and removed with 5% NaOH, and thecopper plated film 52 located under the plated resist 54 is etched witha mixed solution of sulfuric acid and hydrogen peroxide to be dissolvedand removed. As a result, a conductor circuit 58 (including via holes60) constituted by the copper plated film 52 and the electrolytic copperplated film 56, and through holes 46 are formed. Since the through holes46 are formed, no signal line passes through the chip capacitors 20. Inthis manner, there is no problem that the impedance becomesdiscontinuous by the high dielectric body to generate a reflection, andthat the transmission is delayed by passing through the high dielectricbody. An etching solution is sprayed onto both surfaces of the substrateto etch the surface of the conductor circuit 58 and the land surfaces ofthe through holes 46 to form a rough surface 58α over the entire surfaceof the conductor circuit 58 (FIG. 3(D).

(10) A resin filler 62 containing epoxy resin as a main component ischarged into the through holes 46, and is dried (FIG. 4(A)). Instead ofthe resin filler containing epoxy resin as a main component, it is alsopossible to use thermosetting resins, thermoplastic resins, and UV rayhardening resins. Among them, thermosetting resins are preferable,because they are easy to handle when charged into the through holes.

(11) After the foregoing process is finished, a thermosetting epoxyresin sheet having a thickness of 50 μm is vacuum-seal laminated to bothsurfaces of the substrate while raising the temperature in a rangebetween 50 and 150° C. under a pressure of 5 kg/cm² to form aninterlayer resin insulating layer 50 made of epoxy resin (FIG. 4(B)).The degree of vacuum when the vacuum sealing process is performed is 10mmHg. Instead of epoxy resin, olefin resin also may be used.

(12) Openings 148 each having a diameter of 80 μm for via holes areformed in the interlayer resin insulating layer 50 with a CO² gas laserhaving a wavelength of 10.4 μm under conditions that the beam diameteris 5 mm, the mode is the top-hat mode, the pulse width is 5.0μ second,the hole diameter of mask is 0.5 mm, and three shots are performed (FIG.4(C)). Then, a desmear process is conducted using an oxygen plasma.

(13) A plasma treatment is conducted using SV-4540 manufactured byNippon Shinku Gijyutsu Co., Ltd. where the surface of the interlayerresin insulating layer 50 is roughen to form a rough surface 50α (FIG.4(D)). The plasma treatment is conducted using an argon as an inert gaswith an electric power of 200 W under gas pressure of 0.6 Pa at 70° C.for 2 minutes. Instead of the plasma treatment, roughening process maybe conducted using an acid or oxidizer. The rough surface preferably hasa thickness of 0.1 to 5 μm.

(14) The argon gas in the SV-4540 is exchanged with new argon gas, andthe sputtering is conducted using an Ni—Cu alloy as a target in the sameSV-4540 with an electric power of 200 W under a pressure of 0.6 Pa at80° C. for 5 minutes to form an Ni—Cu alloy layer 152 on the surface ofthe interlayer resin insulating layer 50. The Ni—Cu alloy layer 152 hasa thickness of 0.2 μm (FIG. 5(A)). Alternatively, a plated film such asan electroless plated film may be formed, or a plated film may be formedon the sputtered Ni—Cu alloy layer 152.

(15) After the foregoing steps, a commercially available photosensitivedry film is attached on both sides of the substrate 30, and a photo maskfilm is placed thereon. In this state, the substrate 30 is exposed tolight with 100 mJ/cm². Then, the substrate 30 is developed with 0.8%sodium carbonate to form a plated resist 154 having a thickness of 15μm. After that, an electrolytic plating is conducted under the followingconditions to form an electrolytic plated film 156 having a thickness of15 μm (FIG. 5(B)). By this process, the electrolytic plated film 156enlarges the thickness of the portion which will be the conductorcircuit 158 in the step described later and fills and plates the portionwhich will be the via holes 160 in the steps described later. Theadditive added in the electrolytic plating aqueous solution isCaparaside HL produced by Atotech Japan Co., Ltd.

[Electrolytic Plating Aqueous Solution]

sulfuric acid: 2.24 mol/l

copper sulfate: 0.26 mol/l

additive (Caparaside HL produced by Atotech Japan Co., Ltd.): 19.5 mol/l

[Conditions for Electrolytic Plating]

current density: 1 A/dm²

time: 65 minutes

temperature 22±2° C.

(16) The plated resist 154 is peeled and removed in 5% NaOH. After that,the Ni—Cu alloy layer 152 located under the plated resist is dissolvedand removed by etching using sulfuric acid and a mixed solution ofsulfuric acid and hydrogen peroxide. As a result, a conductor circuit158 having a thickness of 16 μm constituted by the Ni—Cu alloy layer 152and the electrolytic plated film 156, and via holes 160 (FIG. 5(C)).

(17) The foregoing steps (11) to (16) are repeated to further forming anupper interlayer resin insulating layer 150 and a conductor circuit 159(including via holes 161) (FIG. 5(D)).

(18) Into a vessel, added are 46.67 parts by weigh of oligomer which isobtained by forming 50% of epoxy groups of 60 weight percent cresolnovolac epoxy resin (manufactured by Nippon Kayaku) dissolved indiethylene glycol dimethyl ether (DMDG) into an acrylic structure andwhich imparts photosensitive characteristic, 15 parts by weight of 80weight percent bisphenol A epoxy resin (Epicoat 1001 manufactured byYuka Shell) dissolved in methylethyl ketone, 1.6 parts by weight ofimidazole hardening agent (2E4MZ-CN manufactured by Shikoku Chemical), 3parts by weight of polyhydric acryl monomer which is a photosensitivemonomer (R604 manufactured by Kyoei Chemical), 1.5 parts by weight ofpolyhydric acryl monomer (DEP6A manufactured by Kyoei Chemical), and0.71 parts by weight of dispersing defoaming agent (S-65 manufactured bySannopuko), and mixed and stirred with one another to prepare a mixedcomposition. Into the mixed composition, added are 2.0 parts by weightof benzophenone (manufactured by Kanto Chemical) serving as aphotoinitiator, and 0.2 parts by weight of Michler's ketone(manufactured for Kanto Chemical) serving as a photosensitizer. Then,the viscosity is adjusted to 2.0 Pa·s at 25° C. so that a solder resistcomposition (i.e. an organic resin insulating material) is obtained.

The viscosity is measured by using No. 4 rotor of a B-type visometer(DVL-B manufactured by Tokyo Keiki) when the velocity is 60 rpm and No.3 rotor of the same when the velocity is 6 rpm.

(19) The solder resist composition is applied to both surfaces of thesubstrate 30 to have a thickness of 20 μm, and is dried at 70° C. for 20minutes and 70° C. for 30 minutes. A photomask having a thickness of 5mm on which a pattern of the solder resist openings are drawn is madehermetic contact and placed onto the solder resist layer 70, and isexposed to light with 1000 mJ/cm². Then, the resultant is developed witha DMTG solution to form openings 71U, 71D each having a diameter of 200μm (FIG. 6(A)). Alternatively, a commercially available solder resistsuch as LPSR may be employed.

(20) The substrate formed with the solder resist layer (i.e. organicresin insulating layer) 70 is immersed into an electroless nickelplating solution containing nickel chloride (2.3×10⁻¹ mol/l), sodiumhypophosphite (2.8×10⁻¹ mol/l), sodium citrate (1.6×10⁻¹ mol/l) andhaving pH of 4.5 for 20 minutes to form a nickel plated layer 72 havinga thickness of 5 μm in the openings 71U, 71D. The resultant substrate isimmersed into an electroless plating solution containing gold potassiumcyanide (7.6×10⁻³ mol/l), ammonia chloride (1.9×10⁻¹ mol/l), sodiumcitrate (1.2×10⁻¹ mol/l), and sodium hypophosphite (1.7×10⁻¹ mol/l) at80° C. for 7.5 minutes to form a gold plated layer 74 having a thicknessof 0.03 μm on the nickel plated layer 72. In this manner, solder pads 75are formed in the via holes 161 and the conductor circuit 159 (FIG.6(B)).

(21) A solder paste is printed in the openings 71U, 71D of the solderresist layer 70, and is reflowed at 200° C. to form solder bumps (solderbodies) 76U, 76D. In this manner, the printed circuit board 10 havingthe solder bumps 76U, 76D is obtained (FIG. 7).

Next, a method for mounting an IC chip onto the printed circuit board 10obtained in the foregoing steps, and a method for attaching the printedcircuit board 10 onto a daughter board will be described with referenceto FIG. 8. An IC chip 90 is placed on the printed circuit board 10 insuch a manner that the solder pads 92 of the IC chip 90 corresponds tothe solder bumps 76U of the printed circuit board 10, and is reflowed.As a result, the IC chip 90 is mounted on the printed circuit board 10.Similarly, the printed circuit board 10 is placed on the daughter board95 in such a manner that the pads 94 of the daughter board 95corresponds to the solder bumps 76D of the printed circuit board 10, andis reflowed. As a result, the printed circuit board 10 is attached tothe daughter board 95.

The above-described resin film contains a refractory resin, solubleparticles, a hardening agent, and other components. Hereinafter, each ofthem will be described.

The resin film used in the manufacturing method of the present inventionhas a structure in that particles soluble in acid or an oxidizer(hereinafter, referred to as “soluble particles”) are dispersed in resinwhich is refractory with respect to acid or an oxidizer (hereinafter,referred to as “refractory resin”).

The expressions “refractory” and “soluble” will now be described. Whenmaterials are immersed in solution composed of the same acid or the sameoxidizers for the same time, a material of a type which is dissolved ata relatively high dissolving rate is called a “soluble” material forconvenience. A material of a type which is dissolved at a relativelyslow dissolving rate is called a “refractory material” for convenience.

The soluble particles are exemplified by resin particles which aresoluble in acid or an oxidizer (hereinafter called “soluble resinparticles”), inorganic particles which are soluble in acid or anoxidizer (hereinafter called “inorganic soluble particles”) and metalparticles which are soluble in acid or an oxidizer (hereinafter called“soluble metal particles”). The foregoing soluble particles may beemployed solely or two or more particles may be employed.

The shape of each of the soluble particles is not limited. The shape maybe a spherical shape or a pulverized shape. It is preferable that theparticles have a uniform shape. The reason for this lies in that a roughsurface having uniformly rough pits and projections can be formed.

It is preferable that the mean particle size of the soluble particles is0.1 μm to 10 μm. When the particles have the diameters satisfying theforegoing range, particles having two or more particle sizes may beemployed. That is, soluble particles having a mean particle size of 0.1μm to 0.5 μm and soluble particles having a mean particle size of 1 μmto 3 μmm may be mixed. Thus, a more complicated rough surface can beformed. Moreover, the adhesiveness with the conductor circuit can beimproved. In the present invention, the particle size of the solubleparticles is the length of a longest portion of each of the solubleparticles.

The soluble resin particles may be particles constituted bythermosetting resin or thermoplastic resin. When the particles areimmersed in solution composed of acid or an oxidizer, the particles mustexhibit dissolving rate higher than that of the foregoing refractoryresin.

Specifically, the soluble resin particles are exemplified by particlesconstituted by epoxy resin, phenol resin, polyimide resin, polyphenyleneresin, polyolefin resin or fluorine resin. The foregoing material may beemployed solely or two or more materials may be mixed.

The soluble resin particles may be resin particles constituted byrubber. Rubber above is exemplified by polybutadiene rubber, a varietyof denatured polybutadiene rubber, such as denatured epoxy rubber,denatured urethane rubber or denatured (metha) acrylonitrile rubber, and(metha) acrylonitrile butadiene rubber containing a carboxylic group.When the foregoing rubber material is employed, the soluble resinparticles can easily be dissolved in acid or an oxidizer. That is, whenthe soluble resin particles are dissolved with acid, dissolution ispermitted with acid except for strong acid. When the soluble resinparticles are dissolved, dissolution is permitted with permanganatewhich has a relatively weak oxidizing power. When chromic acid isemployed, dissolution is permitted even at a low concentration.Therefore, retention of the acid or the oxidizer on the surface of theresin can be prevented. When a catalyst, such as palladium chloride, issupplied after the rough surface has been formed as described later,inhibition of supply of the catalyst and oxidation of the catalyst canbe prevented.

The inorganic soluble particles are exemplified by particles made of atleast a material selected from a group consisting of an aluminumcompound, a calcium compound, a potassium compound, a magnesium compoundand a silicon compound.

The aluminum compound is exemplified by alumina and aluminum hydroxide.The calcium compound is exemplified by calcium carbonate and calciumhydroxide. The potassium compound is exemplified by potassium carbonate.The magnesium compound is exemplified by magnesia, dolomite and basicmagnesium carbonate. The silicon compound is exemplified by silica andzeolite. The foregoing material may be employed solely or two or morematerials may be mixed.

The soluble metal particles are exemplified by particles constituted byat least one material selected from a group consisting of copper,nickel, iron, zinc, lead, gold, silver, aluminum, magnesium, potassiumand silicon. The soluble metal particles may have surfaces coated withresin or the like in order to maintain an insulating characteristic.

When two or more types of the soluble particles are mixed, it ispreferable that the combination of the two types of soluble particles iscombination of resin particles and inorganic particles. Since each ofthe particles has low conductivity, an insulating characteristic withthe resin film can be maintained. Moreover, the thermal expansion caneasily be adjusted with the refractory resin. Thus, occurrence of acrack of the interlayer resin insulating layer constituted by the resinfilm can be prevented. Thus, separation between the interlayer resininsulating layer and the conductor circuit can be prevented.

The refractory resin is not limited when the resin is able to maintainthe shape of the rough surface when the rough surface is formed on theinterlayer resin insulating layer by using acid or oxidizer. Therefractory resin is exemplified by thermosetting resin, thermoplasticresin and their composite material. As an alternative to this, theforegoing photosensitive resin of a type having photosensitivecharacteristic imparted thereto may be employed. When the photosensitiveresin is employed, exposure and development processes of the interlayerresin insulating layers can be performed to form the openings for thevia holes.

In particular, it is preferable that the resin containing thermosettingresin is employed. In the foregoing case, the shape of the rough surfacecan be maintained against plating solution and when a variety of heatingprocesses are performed.

The refractory resin is exemplified by epoxy resin, phenol resin,phenoxy resin, polyimide resin, polyphenylene resin, polyolefin resinand fluorine resin. The foregoing material may be employed solely or twoor more types of the materials may be mixed.

It is preferable that epoxy resin having two or more epoxy groups in onemolecule thereof is employed. The reason for this lies in that theforegoing rough surface can be formed. Moreover, excellent heatresistance and the like can be obtained. Thus, concentration of stressonto the metal layer can be prevented even under a heat cycle condition.Thus, occurrence of separation of the metal layer can be prevented.

The epoxy resin is exemplified by cresol novolac epoxy resin,bisphenol-A epoxy resin, bisphenol-F epoxy resin, phenol novolac epoxyresin, alkylphenol novolac epoxy resin, biphenol-F epoxy resin,naphthalene epoxy resin, dicyclopentadiene epoxy resin, an epoxymaterial constituted by a condensation material of phenol and anaromatic aldehyde having a phenol hydroxyl group, triglycidylisocyanurate and alicyclic epoxy resin. The foregoing material may beemployed solely or two or more material may be mixed. Thus, excellentheat resistance can be realized.

It is preferable that the soluble particles in the resin film accordingto the present invention are substantially uniformly dispersed in therefractory resin. The reason for this lies in that a rough surfacehaving uniform pits and projections can be formed. When via holes andthrough holes are formed in the resin film, adhesiveness with the metallayer of the conductor circuit can be maintained. As an alternative tothis, a resin film containing soluble particles in only the surface onwhich the rough surface is formed may be employed. Thus, the portions ofthe resin film except for the surface is not exposed to acid or theoxidizer. Therefore, the insulating characteristic between conductorcircuits through the interlayer resin insulating layer can reliably bemaintained.

It is preferable that the amount of the soluble particles which aredispersed in the refractory resin is 3 wt % to 40 wt % with respect tothe resin film. When the amount of mixture of the soluble particles islower than 3 wt %, the rough surface having required pits andprojections cannot be formed. When the amount is higher than 40 wt %,deep portions of the resin film are undesirably dissolved when thesoluble particles are dissolved by using acid or the oxidizer. Thus, theinsulating characteristic between the conductor circuits through theinterlayer resin insulating layer constituted by the resin film cannotbe maintained. Thus, short circuit is sometimes is caused to occur.

It is preferable that the resin film contains a hardening agent andother components as well as the refractory resin.

The hardening agent is exemplified by an imidazole hardening agent, anamine hardening agent, a guanidine hardening agent, an epoxy adduct ofeach of the foregoing hardening agents, a microcapsule of each of theforegoing hardening agents and an organic phosphine compound, such astriphenylphosphine or tetraphenyl phosphonium tetraphenyl borate.

It is preferable that the content of the hardening agent is 0.05 wt % to10 wt % with respect to the resin film. When the content is lower than0.05 wt %, the resin film cannot sufficiently be hardened. Thus,introduction of acid and the oxidizer into the resin film occursgreatly. In the foregoing case, the insulating characteristic of theresin film sometimes deteriorates. When the content is higher than 10 wt%, an excessively large quantity of the hardening agent componentsometimes denatures the composition of the resin. In the foregoing case,the reliability sometimes deteriorates.

The other components are exemplified by an inorganic compound which doesnot exert an influence on the formation of the rough surface and afiller constituted by resin. The inorganic compound is exemplified bysilica, alumina and dolomite. The resin is exemplified by polyimideresin, polyacrylic resin, polyamideimide resin, polyphenylene resin,melanine resin and olefin resin. When any one of the foregoing fillersis contained, conformity of the thermal expansion coefficients can beestablished. Moreover, heat resistance and chemical resistance can beimproved. As a result, the performance of the printed circuit board canbe improved.

The resin film may contain solvent. The solvent is exemplified byketone, such as acetone, methylethylketone or cyclohexane; aromatichydrocarbon, such as ethyl acetate, butyl acetate, cellosolve acetate,toluene or xylene. The foregoing material may be employed solely or twoor more materials may be mixed.

First Modification of First Embodiment

A printed circuit board 110 according to a first modification of thefirst embodiment of the present invention will be described withreference to FIG. 15. In the foregoing first embodiment, the BGA isprovided. The first modification of the first embodiment has a structuresimilar to that according to the first embodiment, except that a PGAmethod is employed with which connection is established throughconductive connection pins 96 as shown in FIG. 15.

A method for manufacturing the printed circuit board described abovewith reference to FIG. 15 will be described referring to FIGS. 9 to 15.

(1) Four prepregs 33 impregnated with an epoxy resin are laminated ontop of each other to form a laminated plate 31 a, and a penetratingopening 37 a for accommodating chip capacitors is formed in thelaminated plate 31 a. On the other hand, two prepregs 33 are laminatedon top of each other to form a laminated plate 31 b (FIG. 9(A)). Theprepreg 33 may be impregnated with, instead of the epoxy resin, BT,phenolic resin, or reinforcement material such as glass cloth.

By forming the penetrating opening 37 a for accommodating chipcapacitors in such a manner as to have a large area, a plurality of chipcapacitors 20 can be accommodated in a cavity 37 assuredly in the stepdescribed later.

(2) The laminated plates 31 a and 31 b are vacuum-seal laminated to eachother, and are heated and cured. As a result, a core substrate 31 formedwith the cavity 37 capable of accommodating a plurality capacitors 20 isobtained (FIG. 9(B)).

(3) An adhesive material 34 is applied with a printer to positions onthe cavity 37 where the capacitors 20 will be mounted. Then, a pluralityof chip capacitors 20 made of ceramic are accommodated in the cavity 37via the adhesive material 34 (FIG. 9(C)). By placing a plurality of chipcapacitors 20 in the cavity 37, the plurality of chip capacitor 20 arealigned into the same heights with each other. Thus-obtained coresubstrate 31 has a flat and smooth surface. In addition, since thecavity 37 has a large area, the chip capacitors 20 can be located ataccurate positions with high density. In this manner, a resin layer canbe formed on the core substrate into a uniform thickness, therebyproperly forming via holes in the core substrate 31 as will be describedlater. As a result, the rate of generating defective printed circuitboards can be lowered.

(4) The top surfaces of the chip capacitors 20 are pushed or tapped toalign the chip capacitors 20 into the same heights with each other (FIG.9(D)). By this process, even if chip capacitors 20 having largelydifferent sizes from each other are provided in the cavity 37, they arealigned into the completely same heights with each other. As a result,the core substrate 31 can has a flat and smooth surface.

(5) After that, a thermosetting resin is charged into the space betweenthe chip capacitors 20 in the cavity 37, and then is heated and cured toform a resin layer 36 (FIG. 10(A)). The thermosetting resin ispreferably selected from the group consisting of epoxy, phenol,polyimide, and triazine. In this manner, the chip capacitors 20 can befixed in the cavity 37.

(6) Onto thus-obtained structure, a resin selected from theabove-described epoxy resins and polyolefin resins is applied with aprinter to form a resin insulating layer 40 (FIG. 10(B)). Instead ofapplying the resin, a resin film may be attached.

(7) After that, openings 48 for via holes are formed in the resininsulating layer 40 by exposure to light and development or a laser(FIG. 10(C)). Then, penetrating openings 46 a for through holes areformed in the resin layer 36 with a drill or a laser, and the resinlayer 36 is heated and dried (FIG. 10(D)).

(8) A palladium catalyst is provided to the substrate 31, and then, thecore substrate is immersed into an electroless plating solution touniformly precipitate an electroless plated film 53 (FIG. 11(A)). In theforegoing case, an electroless plating is employed. As an alternative tothis, a metal layer of copper, nickel and the like may be formed bysputtering. As the case may be, an electroless plated film may be formedon the metal layer after the formation of the metal layer by sputtering.

(9) A photosensitive dry film is attached on the surface of theelectroless plated film 53, and a mask is placed thereon. In this state,exposure to light and development are conducted to form a resist 54having a predetermined pattern. The resultant core substrate 31 isimmersed into an electrolytic plating solution, and a current is allowedto flow into the core substrate 31 through the electroless plated film53 to precipitate the electrolytic plated film 56 (FIG. 11(B)).

(10) After the foregoing processes, the resist 54 is peeled and removedwith 5% NaOH, and the copper plated film 53 located under the platedresist 54 is etched with a mixed solution of sulfuric acid and hydrogenperoxide to be dissolved and removed. As a result, a conductor circuit58 (including via holes 60) constituted by the electroless plated film53 and the electrolytic copper plated film 56, and through holes 46 areformed. Since the through holes 46 are formed, no signal line passesthrough the chip capacitors 20. In this manner, there is no problem thatthe impedance becomes discontinuous by the high dielectric body togenerate a reflection, and that the transmission is delayed by passingthrough the high dielectric body.

(11) The substrate 31 is cleaned with water and is degreased with acid,and then, is subjected to soft etching. After that, etching solution issprayed to both surfaces of the substrate 31 so that the surface of theconductor circuit 58 and the surface of each land of each through hole46 are etched. Thus, a rough surface 58 α is formed over the entiresurface of the conductor circuit 58 (FIG. 11(C)). The etching solutionis mixed solution of 10 parts by weight of copper (II) imidazolecomplex, 7 parts by weight of glycolic acid, and 5 parts by weight ofpotassium chloride (Mech etch bond, manufactured by Mech Co., Ltd.).

(12) Into a container, added are 100 parts by weight of bisphenol-Fepoxy monomer (YL983U having a molecular weight of 310, manufactured byYuka Shell), 170 parts by weight of SiO₂ spherical particles (CRS1101-CEmanufactured by Adotech) having surfaces each of which is coated with asilane coupling agent and a mean particle size of 1.6 μm and structuredsuch that the diameter of the largest particle is 15 μm or smaller, and1.5 parts by weight of leveling agent (Pelenol S4 manufactured bySannopuko). These materials are stirred and mixed to prepare a resinfiller 62 having a viscosity of 45 to 49 Pa·s at 23±1° C. As a hardeningagent, 6.5 parts by weight of imidazole hardening agent (2E4MZ-CNmanufactured by Shikoku Kasei) is employed.

The resin filler 62 is charged into each through hole 46, and is dried(FIG. 11(D)).

(13) 30 parts by weight of bisphenol-A epoxy resin

(Epicoat 1001 having an epoxy equivalent of 469, manufactured by YukaShell), 40 parts by weight of cresol novolac epoxy resin (Epichron N-673having an epoxy equivalent of 215, manufactured by Dainippon Ink &Chremicals), 30 parts by weight of phenol novolac resin containing atriazine structure (Phenolight KA-7052 having a phenol hydroxyl groupequivalent of 120, manufactured by Dainippon Ink & Chemicals) are heatedand dissolved in 20 parts by weight of ethyldiglycol acetate and 20parts by weight of solvent naphtha while being stirred. Then, 15 partsby weight of polybutadine rubber having epoxy terminal (Denalex R-45EPTmanufactured by Nagase Chemicals), 1.5 parts by weight of pulverized2-phenyl-4,5-bis(hydroxymethyl) imidazole, 2 parts by weight ofparticle-seize reduced silica, and 0.5 parts by weight of silicondefoaming agent are added to prepare 0.5 parts by weight of epoxy resincomposition.

The obtained epoxy resin composition is applied onto a PET film having athickness of 38 μm using a roll coater such that the thickness after thePET film is dried is 50 μm. Then, drying is performed at 80 to 120° C.for 10 minutes. Thus, a resin film for the interlayer resin insulatinglayer is manufactured.

(14) Thus-manufactured resin film for the interlayer resin insulatinglayer is placed on the substrate 31 manufactured in the above step (13).In this case, the resin film has a size slightly larger than thesubstrate 31. Then, temporal pressing is performed under conditions thatthe pressure is 4 kgf/cm², the temperature is 80° C., and the pressingduration is 10 seconds, and then, cutting is performed. After that, avacuum laminator apparatus is operated to bond the resin film by thefollowing method thereby forming an interlayer resin insulating layer 50(FIG. 12(A)). That is, main pressing of the resin film for theinterlayer resin insulating layer to the surface of the substrate 31 isperformed under conditions that the degree of vacuum is 0.5 Torr, thepressure is 4 kgf/cm², the temperature is 80° C., and the pressingduration is 60 seconds. Then, curing with heat is performed at 170° C.for 30 minutes.

(15) A mask 47 incorporating penetrating openings 47 a formed thereinand having a thickness of 1.2 mm is placed on the interlayer resininsulating layer 50. Then, CO² gas laser beam having a wavelength of10.4 μm is used to form openings 148 for the via holes each having adiameter of 80 μm are formed in the interlayer resin insulating layer 50under conditions that the beam diameter is 4.0 mm, the mode is thetop-hat mode, the pulse width is 8.0 μsec, the diameter of eachpenetrating opening in the mask is 1.0 mm, and one shot is performed(FIG. 12(B)).

(16) The substrate 31 formed with the openings 148 for the via holes isimmersed in solution which contains 60 g/l permanganic acid and has atemperature of 80° C. for 10 minutes so as to dissolve and remove theepoxy resin particles present on the surface of the interlayer resininsulating layer 50. As a result, the surface of the interlayer resininsulating layer 50 including the inner wall of each opening 148 for thevia hole is roughened to be a rough surface 50α (FIG. 12(C)).Alternatively, the surface of the interlayer resin insulating layer 50may be roughened with an acid or an oxidizer. The rough surfacepreferably has a thickness of 0.1 to 5 μm.

(17) The substrate 31 after being subjected to the foregoing process isimmersed in neutral solution (manufactured by Siplay), and then cleanedwith water. The surface of the substrate 31 subjected to the rougheningprocess (depth of roughness is 3 μm) is supplied with palladiumcatalyst. Thus, the catalyst cores are adhered to the surface of theinterlayer resin insulating layer 50 and the inner wall of each opening48 for the via hole.

(18) The substrate is immersed into electroless copper plating solutionhaving the following composition to form an electroless copper platedfilm 153 having a thickness of 0.6 to 3.0 μm over the entire surface ofthe rough surface 50α (FIG. 12(D)).

NiSO₄: 0.003 mol/l

tartaric acid: 0.200 mol/l

copper sulfate: 0.030 mol/l

HCHO: 0.050 mol/l

NaOH: 0.100 mol/l

α′α-bipyridyl: 40 mg/l

polyethylene glycol (PEG): 0.10 mg/l

[Electroless Plating Conditions]

40 minutes in a state where the temperature of the solution is 35° C.

(19) A commercially available photosensitive dry film is bonded to theelectroless copper plated film 153, and a mask is placed thereon. Theresultant is subjected to exposure to light with 100 mJ/cm², and isdeveloped with 0.8% sodium carbonate to form a plating resist 154 havinga thickness of 30 μm (FIG. 13(A)).

(20) The substrate 31 is cleaned with water of 50° C. and is degreased.Then, the substrate 31 is cleaned with water of 25° C., and is furthercleaned with sulfuric acid. After that, an electroplating is performedunder the following conditions to form an electrolytic copper platedfilm 156 having a thickness of 20 μm (FIG. 13(B)).

[Electroplating Solution]

sulfuric acid: 2.24 mol/l

copper sulfate: 0.26 mol/l

additive: 19.5 ml/l

(Kapalacid HL, Manufactured by Atotech Japan)

[Electroplating Conditions]

current density: 1 A/dm²

duration: 65 minutes

temperature: 22±2° C.

(21) The plating resist 154 is peeled and removed with 5% NaOH, and thenthe electroless copper plated film 153 located under the plating resist154 is dissolved and removed by performing etching using mixed solutionof sulfuric acid and hydrogen peroxide. Thus, a conductor circuit 158(including via holes 161) constituted by the electroless copper platedfilm 153 and the electrolytic copper plated film 156 and having athickness of 18 μm is formed. After that, the same process as theprocess (11) is conducted to form a rough surface 158α with an etchingsolution containing cupric complex and an organic acid (FIG. 13(C)).

(22) The foregoing processes (14) to (21) are repeated to furtherforming an upper interlayer resin insulating layer 150 and a conductorcircuit 159 (including via holes 161) (FIG. 13(D)).

(23) By repeating the process of the first embodiment, a solder resistcomposition (i.e. an organic resin insulating material) is obtained.

(24) The solder resist composition prepared in the foregoing process(23) is applied on both sides of the multi-layer printed circuit boardinto a thickness of 20 μm. Then, the resultant is dried and exposed toUV ray, and is developed with a DMTG solution to form openings 71U, 71Deach having a diameter of 200 μm.

Then, a heat process is performed to cure the solder resist composition.As a result, a solder resist layer 70 having the openings 71U, 71D and athickness of 20 μm is formed (FIG. 14(A)). As the solder resistcomposition, it is also possible to use a commercially available solderresist composition.

(25) The substrate formed with the solder resist layer 70 is immersedinto an electroless nickel plating solution of the same type as thatused in the first embodiment to form a nickel plated layer 72 having athickness of 5 μm in the openings 71U, 71D. Thus-formed substrate isimmersed into an electroless gold plating solution of the same type asthat used in the first embodiment to form a gold plated layer 74 havinga thickness of 0.03 μm on the nickel plated layer 72 (FIG. 14(B)).

(26) A solder paste containing tin-lead is printed to each opening 71Uin the solder resist layer 70 on the surface of the substrate on whichthe IC chip is to be mounted. Moreover, a solder paste as a conductiveadhesive 97 is printed to each opening 71D on the other surface of thesubstrate. Conductive connection pins 96 are attached and held to aproper pin holding apparatus so that the fixing section 98 of eachconductive connection pin 96 is brought into contact with the conductiveadhesive 97 in the opening 71D. Then, reflowing is conducted to fix thefixing section 98 of each conductive connection pin 96 to the conductiveadhesive 97. As a method for attaching the conductive connection pins96, the conductive adhesive 97 is formed into the shape of ball, and isinserted into each opening 71D, or alternatively, the conductiveadhesive 97 is bonded to each fixing section 98, and the conductiveconnection pins 96 are attached thereto. After that, reflowing may beconducted.

An IC chip 90 is mounted in such a manner that the solder pads 92 of theIC chip 90 corresponds to the solder bumps 76U on the side of openings71U of the printed circuit board 110. Then, reflowing is conducted toattach the IC chip 90 to the printed circuit board 110 (FIG. 15).

Second Modification of First Embodiment

A method for manufacturing a printed circuit board according to a secondmodification of the first embodiment will be described with reference toFIG. 16.

(1) For prepregs 33 each of which is impregnated with epoxy resin arelaminated and cured to form a laminated plate 31 a. Through openings 37a for accommodating chip capacitors are formed in the laminated plate 31a. On the other hand, a sheet 31 c constituted by an uncured prepreg 33and a plate 31 b constituted by a cured prepreg 33 are prepared (FIG.16(A)).

(2) The laminated plate 31 a and the plate 31 b are press-laminated toeach other to form a substrate 31 having a cavity 37 (FIG. 16(B)).

(3) A plurality of chip capacitors 20 made of ceramic are accommodatedonto the sheet 31 c constituted by the uncured prepreg 33 (FIG. 16(C)).

(4) The top surfaces of the chip capacitors 20 are pushed or tapped toalign the chip capacitors 20 into the same heights with each other (FIG.16(D)). After that, a heat process is performed to cure the uncuredprepreg 33 to form a substrate 31. The subsequent processes are the sameas those of the first modification which has been described above withreference to FIGS. 9 to 15, and therefore, their description will beomitted.

Third Modification of First Embodiment

A structure of a printed circuit board according to a third modificationof the first embodiment will be described referring to FIG. 18.

The printed circuit board according to the third modification has thestructure similar to that of the first embodiment, except for thestructure of the chip capacitors 20 accommodated in the core substrate30. FIG. 18 is a plan view showing the chip capacitors. FIG. 18(A) is adiagram showing a chip capacitor before being cut from which a pluralityof pieces are to be obtained by cutting. In FIG. 18(A), a chain lineshows the cutting line. In the printed circuit board described in thefirst embodiment, as shown in the plan view of FIG. 18(B), the firstelectrodes 21 and the second electrodes 22 are provide along the sideends of the chip capacitor. FIG. 18(C) is a diagram showing a chipcapacitor before being cut from which a plurality of pieces are to beobtained by cutting according to the third modification. In FIG. 18(C),a chain line shows the cutting line. In the printed circuit boarddescribed in the third modification, as shown in the plan view of FIG.18(D), the first electrodes 21 and the second electrodes 22 are provideinside the side ends of the chip capacitor.

In the printed circuit board according to the third modification, thechip capacitor 20 in which the electrodes are formed along an inside ofthe outer edge thereof is used. Therefore, a chip capacitor having alarge capacity can be used as the chip capacitor 20.

A printed circuit board according to first alternative example of thethird modification will be described referring to FIG. 19.

FIG. 19 is a diagram showing a plan view of the chip capacitor 20 to beaccommodated in the core substrate of the printed circuit boardaccording to a first alternative example. In the above-described firstembodiment, a plurality of chip capacitors each having a small capacityare accommodated in the core substrate. Contrary to this, in the firstalternative example, a large chip capacitor having a large capacity isaccommodated in the core substrate. The chip capacitor 20 includes firstelectrodes 21, second electrodes 22, a dielectric body 23, a firstconductive firm 24 connected to the first electrodes 21, a secondconductive film 25 connected to the second electrodes 22, and electrodes27 which are not connected to the first conductive film 24 and thesecond conductive film 25 and used for connecting the upper and lowersurfaces of the chip capacitor. The chip capacitor is connected to theIC chip and the daughter board through the electrodes 27.

In the printed circuit board according to the first alternative example,the chip capacitor 20 having a large size is used. Therefore, a chipcapacitor having a large capacity can be employed as the chip capacitor20. In addition, the use of large-sized chip capacitor 20 prevents thewarpage of the printed circuit board even if the printed circuit boardis repeatedly subjected to heat cycle.

Next, a printed circuit board according to a second alternative examplewill be described referring to FIG. 20. FIG. 20(A) is a diagram showinga chip capacitor before being cut from which a plurality of pieces areto be obtained by cutting. In FIG. 20(A), a chain line shows the cuttingline. FIG. 20(B) is a diagram showing a plan view of the chip capacitor.In the second alternative example, as shown in FIG. 20(B), a pluralityof chip capacitors from each of which a plurality of pieces are to beobtained by cutting (in FIG. 20(B), three pieces) are connected into onepiece unit having a large size.

In the second alternative example, the chip capacitor 20 having a largesize is used. Therefore, a chip capacitor having a large capacity can beemployed as the chip capacitor 20. In addition, the use of large-sizedchip capacitor 20 prevents the warpage of the printed circuit board evenif the printed circuit board is repeatedly subjected to heat cycle.

In the above-described embodiment, the chip capacitor is incorporated inthe printed circuit board. Instead of the chip capacitor, it is alsopossible to use a plate-like capacitor in which a conductive film isformed on a ceramic plate.

Fourth Modification of First Embodiment

A printed circuit board according to a fourth modification of the firstembodiment will be described with reference to FIG. 21. In theabove-described first embodiment, the printed circuit board is providedwith the chip capacitors 20 in the core substrate 30 alone. In thefourth modification, chip capacitors 120 having a large capacity aremounted on the surface of the printed circuit board.

The IC chip conducts a complicated calculation, and in the calculationprocessing, it instantaneously consumes a large electric power. In orderto provide a large electric power to the IC chip, in this embodiment,chip capacitor 20 for power supply and chip capacitors 120 are providedto the printed circuit board. The effect of providing the chipcapacitors 20 and 120 will be described with reference to FIG. 22.

In the graph of FIG. 22, a longitudinal axis indicates a voltagesupplied to the IC chip, and a horizontal axis indicates a time. Thechain double-dashed line C indicates the variation in the voltagesupplied to the printed circuit board having no capacitor for powersource. Without capacitor for power supply, the voltage is drasticallyattenuated. The broken line A indicates the variation in the voltagesupplied to the printed circuit board having a chip capacitor on itssurface. As compared with the case of the printed circuit board havingno capacitor indicated by the chain double-dashed line C, theattenuation of voltage is not large. However, the length of loop becomeslarge, and sufficient electric power cannot be supplied in the ratedetermining step. That is, the voltage drastically drops down at thetime of starting the supply of electric power. The chain double-dashedline B, referring to FIG. 8, indicates the voltage drop of the printedcircuit board incorporating the chip capacitor. Whereas the length ofthe loop can be shortened, the voltage varies because a chip capacitorhaving a large capacitor cannot be accommodated on the core substrate30. The solid line E indicates the variation in the voltage of theprinted circuit board according to the fourth modification having chipcapacitors 20 in its core substrate described above referring to FIG.21, and the chip capacitors 120 having a large capacitor on its surface.The printed circuit board is provided with the chip capacitors 20 in thevicinity of the IC chip, and the chip capacitors 120 having a largecapacity (and a relatively large inductance), thereby suppressing thevariation in voltage to a minimum value.

As to the printed circuit board of the first embodiment, the inductanceof the chip capacitors 20 embedded in the core substrate, and theinductance of the chip capacitors mounted on the back surface of theprinted circuit board (on the surface at the side of daughter board) areshown as follows.

In the case of a single capacitor:

A capacitor of embedded type: 137 pH

A capacitor of back surface mounted type: 287 pH

In the case of eight capacitors connected in parallel:

Capacitors of embedded type: 60 pH

Capacitors of back surface mounted type: 72 pH

In both cases where a single capacitor is used and where a plurality ofcapacitors are connected in parallel to obtain an increased capacity, aninductance can be lowered by incorporating the chip capacitor.

Hereinafter, the results of reliability test will be described. In thetest, the rate of change in the electrostatic capacity of a single chipcapacitor in the printed circuit board of the first embodiment wasmeasured.

Rate of change in electrostatic capacity (measured at a frequency of 100Hz (measured at a frequency of 1 kHz)

Steam 168 hours: 0.3% 0.4% HAST 100 hours: −0.9% −0.9% TS 1000 cycles:1.1% 1.3%

In the Steam test, the chip capacitor was subjected to steam to be keptat a moisture of 100%. In the HAST test, the chip capacitor was left for100 hours at a relative moisture of 100%, an applied voltage of 1.3V,and at a temperature of 121° C. In the TS test, the chip capacitor wasleft for 30 minutes at −125° C., and 30 minutes for 55° C., and thistest was repeated 1000 times.

In the above-described reliability test, it was realized that theprinted circuit board incorporating the chip capacitors attains areliability of the same level as the conventional printed capacitor onwhich a capacitor is mounted on its surface. As described above, in theTS test, even if an internal stress is generated due to the differencein the thermal expansion coefficients between the capacitor made ofceramic, and the core substrate 30 and the resin insulating layer 40made of resin, no problems are created such as a disconnection betweenthe first electrode 21, the second electrode 22 of the chip capacitor20, and the via holes 60, a peeling of the chip capacitors 20 from theresin insulating layer 40, and the cracks in the resin insulating layer40. In this manner, high reliability can be attained over a long periodof time.

In the first embodiment, as described above, a large cavity is formedand a plurality of capacitors are accommodated in the cavity. Thisstructure makes it possible that the plurality of capacitors arereliably aligned at accurate positions on the core substrate with highdensity even if accuracy of the spot-facing process is low. In addition,the plurality of capacitors are placed in the cavity, the capacitors arealigned into the same heights with each other. Therefore, the insulatinglayer can be formed on the capacitors into a uniform thickness. The viaholes and the conductor circuit can be properly formed, and the rate ofgenerating defective printed circuit boards 10 can be lowered.

Since the resin is charged in the space between the core substrate andthe capacitor, even if the stress is generated caused by the capacitors,the stress can be alleviated. In addition, no migration is created. As aresult, neither peeling nor dissolution is caused between the electrodesof the capacitors and the connecting sections of the via holes. Due tothese arrangements, the desired performance can be maintained in thereliability test. In the case where the capacitors are coated withcopper, the generation of migration can be prevented.

Second Embodiment

First, the structure of a printed circuit board according to a secondembodiment of the present invention will be described with reference toFIGS. 29 and 30. FIG. 29 is a diagram showing a cross-section of aprinted circuit board 210. FIG. 30 is a diagram showing the state wherean IC chip 290 is mounted on the printed circuit board 210 shown in FIG.29, and the printed circuit board 210 is attached to a daughter board294.

As shown in FIG. 29, the printed circuit board 210 incorporates chipcapacitors 220, a core substrate 230 for accommodating chip capacitors220, and an interlayer resin insulating layer 250 constituting thebuildup layers 280A, 280B. The core substrate 230 is constituted by anaccommodating layer 230 a for accommodating the capacitors 220, and aconnection layer 240. Via holes 260 and a conductor circuit 258 areformed in the connection layer 240. Via holes 360 and a conductorcircuit 358 are formed in the interlayer resin insulating layer 250. Inthis embodiment, the buildup layer is constitute by a single interlayerresin insulating layer 250. As an alternative to this, the buildup layermay be constituted by a plurality of interlayer resin insulating layers.

As shown in FIG. 30, the via holes 360 in the upper buildup layer 280Aare formed with bumps 276 to be respectively connected to pads 292S1,292S2, 292P1, 292P2 of the IC chip 290. On the other hand, the via holes360 in the lower buildup layer 280B are formed with bumps 276 to berespectively connected to pads 295S1, 295S2, 295P1, 295P2. Through holes246 are formed in the core substrate 230.

As shown in FIG. 17(A). the chip capacitor 220 is constituted by a firstelectrode 221, a second electrode, 222, and an dielectric body 23interposed between the first and second electrodes. The dielectric body23 includes a plurality of first conductive films 24 connected to thefirst electrode 221 and a plurality of second conductive films 25connected to the second electrode 222 in an opposed relation to eachother. It is preferable to cover the surfaces of the first electrode 221and the second electrode 222 with an metallic coating such as copperplating. By coated with the metallic coating, the electric connectionwith the conductive adhesive 234 is improved, and the generation ofmigration can be prevented.

As shown in FIG. 30, The pad 292S2 for signal of the IC chip 290 isconnected to the pad 295S2 for signal of the daughter board 294 throughthe bump 276-the conductor circuit 358-the via hole 360-the through hole246-the via hole 360-the bump 276. On the other hand, the pad 292S1 forsignal of the IC chip 290 is connected to the pad 295S1 for signal ofthe daughter board 294 through the bump 276-the via hole 360-the throughhole 246-the via hole 360-the bump 276.

The pad 292P1 for power supply of the IC chip 290 is connected to thefirst electrode 221 of the chip capacitor 220 through the bump 276-thevia hole 360-the conductor circuit 258-the via hole 260. On the otherhand, the pad 295P1 for power supply of the daughter board 294 isconnected to the first electrode 221 of the chip capacitor 220 throughthe bump 276-the via hole 360-the through hole 246-the conductor circuit258-the via hole 260.

The pad 292P2 for power supply of the IC chip 290 is connected to thesecond electrode 222 of the chip capacitor 220 through the bump 276-thevia hole 360-the conductor circuit 258-the via hole 260. On the otherhand, the pad 295P2 for power supply of the daughter board 294 isconnected to the second electrode 222 of the chip capacitor 220 throughthe bump 276-the via hole 360-the through hole 246-the conductor circuit258-the via hole 260.

In the printed circuit board 210 of this embodiment, the chip capacitors220 are placed immediately below the IC chip 290. The distance from theIC chip to each capacitor is shortened, and therefore, electric powercan be instantaneously supplied to the IC chip. That is, the loop lengthwhich determines the loop inductance can be shortened.

In addition, the through hole 246 is formed between the chip capacitors220, and no signal line passes through the chip capacitors 220. In thisstructure, there is no problem that the impedance becomes discontinuousby the high dielectric body to generate a reflection, and that thetransmission is delayed by passing through the high dielectric body.

The external substrate (i.e. daughter board) 294 to be connected to theback surface of the printed circuit board is connected to the firstelectrode 221 and the second electrode 222 of the capacitor 220 throughthe via hole 260 formed in the connection layer 240 on the side of ICchip and the through hole 246 formed in the core substrate 230. That is,although the accommodation layer 230 a having a core material is hard toprocess, penetrating openings are formed in the accommodation layer 230a so that the terminal of the capacitor is not directly connected to theoutside surface. As a result, the reliability of the connection can beincreased.

As shown in FIG. 17(A), in this embodiment, a rough surface 23α isformed on the surface of the dielectric body 23 made of ceramic of thechip capacitor 220. The rough surface 23α contributes to an increasedadhesion between the chip capacitor 220 made of ceramic and a resininsulating layer 240 made of resin, thereby avoiding the resininsulating layer 240 from peeling from the interface with the chipcapacitors 220 even when a heat cycle test is conducted. The roughsurface 23α can be formed by polishing the surface of the chip capacitor220 after the sintering step, or by roughening the surface of the chipcapacitor 220 before the sintering step. In this embodiment, the surfaceof the chip capacitor is roughened to increase its adhesion with theresin insulating layer. Alternatively, the surface of the chip capacitormay be subjected to silane coupling process.

In this embodiment, a resin layer 236 is interposed between the sidesurface of the cavity 232 of the core substrate 230 and the chipcapacitor 220. The thermal expansion coefficients of the resin layer 236is set to the value lower than those of the core substrate 230 and theresin insulating layer 240, that is, are set to the value close to thatof the chip capacitor 220 made of ceramics. In this manner, even ifinternal stress is generated between the core substrate 220 and theresin insulating layer 240, and the chip capacitor 20 caused by thedifference in the thermal expansion coefficients therebetween, cracksand peelings do not easily occur in the core substrate 230 and theconnection layer 240. As a result, high reliability can be attained. Inaddition, the generation of migration can be prevented.

Next, the method for manufacturing the printed circuit board describedabove referring to FIG. 29 will be described with reference to FIGS. 23to 28.

(1) A connection layer, which is a resin layer constituting the coresubstrate, is formed. On one surface of the connection layer, a circuitpattern constituted by a metallic layer is formed. For this purpose, aresin film 240 a having a metal film 257 laminated on its one surface isprepared (FIG. 23(A)). The resin film 240 a may be made of, as is thecase of the first embodiment, thermosetting resin such as epoxy, BT,polyimide, and olefin, or mixtures of thermosetting resins andthermoplastic resins. In this embodiment, it is preferable to use a filmhaving no core material so that the penetrating openings can be easilyformed. The metal film 257 is pattern-etched to form a predeterminedcircuit pattern 257α (FIG. 23(B)). The chip capacitors 220 are attachedto the circuit pattern 257α located on the lower surface of the resinfilm 240 a through the conductive adhesive material 234 c FIG. 23(C)).In this manner, the electrical connection with the capacitors 220 andthe adhesion between the capacitors 220 and the circuit pattern 257α canbe assured. The conductive adhesive material 234 may be a materialhaving both conductivity and adhesiveness such as a solder (Sn/Pb,Sn/Sb, Sn/Ag, Sn/Ag/Cu), conductive pastes, and resins impregnated withmetal particles. The space created between the conductive adhesive andthe capacitor is preferably filled with a resin.

(2) On the other hand, a laminated plate 232 a for accommodation layerformed with cavities 232 for accommodating chip capacitors is prepared(FIG. 23(C)).

The cavities 232 are formed by spot-facing process. Instead ofspot-facing process, the cavities may be formed in the laminated late bybonding a prepreg formed with penetrating openings and a prepreg formedwith no penetrating openings, or by injection molding. The laminatedplate 232 a for accommodation layer may be a laminated plate formed bylaminating prepregs each having a core member such as glass clothimpregnated with an epoxy resin. Instead of the laminated plate having acore member impregnated with epoxy resin, it is also possible to use alaminated plate generally used in a printed circuit board, such as thosehaving a core member impregnated with BT, phenolic resins, or areinforcement member such as glass cloth. It is also possible to use aresin substrate having no core member such as glass cloth. However, itis impossible to use a substrate of ceramic or AIN as the coresubstrate. The substrate of ceramic or AIN is poor in processability forouter shape, and in some cases, is incapable of accommodatingcapacitors. In addition, a space is created inside the substrate even ifit is filled with a resin. Since a resin substrate has a melting pointof 300° C. or lower, it is dissolved or softened when a heat higher than350° C. is applied.

(3) The resin film 240 a to which the chip capacitors 220 are attached,a resin laminated plate 232 a for core substrate having sections foraccommodating capacitors, and another resin film 240 a are laminated toeach other, and are pressed from both sides to flatten the surface (FIG.23(D)). In this embodiment, the accommodation layer 230 a whichaccommodates the capacitors 220 and the connection layer 240 are bondedto each other by application of pressure from both sides to form a coresubstrate 230. As a result, the core substrate 230 has a flat surface.The interlayer resin insulating layer 250 and the conductor circuit 358can be laminated in a later step in such a manner that high reliabilityis attained. At this time, the space between the capacitor 220 and theresin film 240 a is filled with a resin exuding from the resin film 240a. If the space cannot sufficiently filled with the resin, as shown inFIG. 24(A), a small-sized filler 236 a having a thermal expansioncoefficient smaller than that of the core substrate is provided betweenthe circuit patterns 257 α on the side of the resin film 240 a, so thatthe space is filled with the filler 236 a as shown in FIG. 24(D).Alternatively, as shown in FIG. 24(C), the filler 236 a may be placed onthe capacitor 220, so that the space is filled with the filler 236 a asshown in FIG. 24(D).

(4) Heating and curing is conducted to form a core substrate 230constituted by an accommodation layer 230 a accommodating the chipcapacitors 220 and a connection layer (FIG. 25(A)). It is preferablethat a resin layer 236 having a thermal expansion coefficient smallerthan that of the core substrate is charged in the cavity 232 of the coresubstrate to increase the air tightness. In this embodiment, a resinfilm 240 a having no metal layer is laminated. As an alternative tothis, a resin film (RCC) having a metal layer on its one side may beused. That is, it is possible to use a both-sided plate, a one-sidedplate, a resin plate having no metal film, and a resin film.

(5) In this embodiment, a circuit pattern 257 α to be connected to theconductive adhesive 234 is provided between the connection layer 240 andthe accommodating layer 230 which form the core substrate 230 together.With this arrangement, the connection to the capacitors 220 is reliablyestablished through the circuit pattern 257α. In addition, since circuitpattern 257α is provided between the connection layer 240 and theaccommodation layer 230 a, the warpage of the core substrate 230 can beprevented.

(6) Non-penetrating openings 248 to be via holes are formed in the upperconnection layer 240 by CO₂ laser, YAG laser, excimer laser, or UV laser(FIG. 25(B)). As the case may be, an area mask on which penetratingopenings are formed at positions corresponding to the positions of thenon-penetrating openings are mounted, and an area processing isconducted by a laser. In the case where it is desired to form via holeshaving different sizes and diameter from each other, the lasers may beused in combination to form the via holes.

(7) If necessary, smear in the via holes may be conducted by a gasplasma treatment using gaseous matter such as oxygen and nitrogen, ordry treatment such as corona treatment, or by immersion into an oxidizersuch as permagnetic acid. Subsequently, penetrating openings 246 ahaving a diameter of 50 to 500 μm for through holes are penetrated inthe core substrate 230 constituted by the connection layer 240, theaccommodation layer 230 a, and the connection layer 240 by a drill or alaser (FIG. 25(C)).

(8) A metal film is formed on the surface layer of the connection layer240, the non-penetrating openings 248 for via holes, and the penetratingopenings 246 a for through holes of the core substrate 230. For thispurpose, a palladium catalyst is provide on the surface of theconnection layer 240, and then, the core substrate 230 is immersed in anelectroless plating solution to uniformly precipitate an electrolesscopper plated film 252 (FIG. 26(A)). In this embodiment, an electrolessplating is employed. Alternatively, a metal film of copper, nickel andthe like may be formed by sputtering. The sputtering is disadvantageousfrom the viewpoint of cost, but is advantageous in that the adhesionwith the resin film can be improved. An electroless plated film may beformed after the metal layer is formed by sputtering. Depending on thekind of resin, there are cases where the catalyst cannot be stablyprovided thereto. In this case, the electroless plated film is effectivein stably providing the catalyst to such a resin. In addition, theelectrolytic plating is more stably precipitated in the case of formingthe electroless plated film. The metal film 252 is preferably formedinto the thickness of 0.1 to 3 mm.

(9) A photosensitive dry film is attached to the surface of the metalfilm 252, and a mask is placed thereon. Exposure to light anddevelopment are performed to form a resist 254 having a predeterminedpattern. The core substrate 230 is immersed into an electrolytic platingsolution to allow a current to flow in the core substrate 230 throughthe electroless plated film 252 to precipitate an electrolytic copperplated film 252 (FIG. 26(B)). The resist 254 is peeled by 5% KOH, andthen, the electroless plated film 252 located under the resist 254 isetched and removed by a mixed solution of sulfuric acid and hydrogenperoxide. As a result, via holes 260 and a conductor circuit 258 areformed in the connection layer 240, and through holes 246 are formed inthe penetrating openings 246 a of the core substrate 230 (FIG. 26(C)).

(10) A rough surface is formed on the surface of the conductive layer ofthe conductor circuit 258, the via holes 260, and the through holes 246.The rough surface is formed by oxidizing (i.e. blacking)-reductiontreatment, an electroless plated film made of alloys of Cu—Ni—P, or byetching treatment using an etching solution containing cupric complexand an organic acid. The rough surface has Ra (mean roughness height) of0.01 to 5 μm, and especially preferable is Ra of 0.5 to 3 μm. In thisembodiment, the rough surface is formed. Alternatively, as will bedescribed later, a resin is directly filled and a resin film may beattached.

(11) The through holes 246 are filled with a resin layer 262. The resinlayer may be made of a resin having no conductivity and containing aepoxy resin as a main component, or a resin having conductivity andcontaining a paste of metal such as copper. In this case, thethermosetting epoxy resin containing a silica for adjusting the thermalexpansion coefficient is charged as a resin filler. After the throughholes 246 are filled with the resin layer 262, the resin film 250 isattached (FIG. 27(A)). Instead of attaching the resin film 250, a resinmay be applied. After the resin film 250 is attached, via holes 348having an opening diameter of 20 to 250 μm are formed in the insulatinglayer 250, and thermosetting is conducted (FIG. 27(B)). Then, a catalystis provided to the core substrate, and the core substrate is immersed inelectroless plating to uniformly precipitate an electroless plated film352 having a thickness of 0.9 μm on the surface of the interlayer resininsulating layer 250. After that, a resist 354 having a predeterminedpattern is formed (FIG. 27(C)).

(12) The core substrate is immersed in an electrolytic plating solutionto allow a current to flow in the core substrate through the electrolessplated film 352 to form an electrolytic copper plated film 356 in theportions where no resist 354 is formed (FIG. 28(A)). The resist 354 ispeeled and removed, and then, the electroless plated film 352 locatedunder the plated resist is dissolved and removed to obtain a conductorcircuit 358 constituted by the electroless plated film 352 and theelectrolytic copper plated film 356 and via holes 360 (FIG. 28(B)).

(13) A rough surface (not shown) is formed on the surface of theconductor circuit 358 and the via holes 360 by an etching solutioncontaining cupric complex and an organic acid. It is also possible tofurther performing Sn substitution on the rough surface.

(14) Solder bumps are formed on the above-described printed circuitboard. On both sides of the substrate, a solder resist composition isapplied, and drying is performed. After that, a photomask film (notshown) on which a circular pattern (i.e. mask pattern) is drawn is madehermetic contact and placed onto the solder resist composition, and isexposed to UV ray and then is developed. Furthermore, heating isperformed to form a solder resist layer (having a thickness of 20 μm)having openings 271U, 271D at solder pad portions (including via holesand land portions thereof) (FIG. 28(C)).

(15) The openings 271U, 271D of the solder resist layer 270 are filledwith a solder paste (not shown). Then, the solder charged into theopenings 271U, 271D is relowed at 200° C. to form solder bumps (i.e.solder bodies) 276 are formed (FIG. 29). In order to increase thecorrosion resistance, a layer of metal such as Ni, Au, Ag, Pd and thelike may be formed in the opening 271 by plating or sputtering.

The processes of mounting the IC chip on the printed circuit board, andattaching the printed circuit board to the daughter board are the sameas those of the first embodiment, and their description will be omitted.

First Modification of Second Embodiment

A printed circuit board according to a first modification of the secondembodiment will be described with reference to FIG. 31. The printedcircuit board according to a first modification has a similar structureas of second modification, except for the following points. That is, inthe printed circuit board of the first modification, conductive pints296 are provided, and a connection with the daughter board isestablished through the conductive pins 296. Whereas the resin film 240a having the metal film 257 on its one side is employed in the foregoingembodiment described above referring to FIG. 23(A), in the firstmodification, a resin film having metal films on its both sides isemployed to manufacture an interlayer resin insulating layer 240 on theside of IC chip 290. That is, the upper metal film is pattern-etched toform a circuit pattern 257α. Furthermore, non-penetrating openings 248are formed by a laser to form via holes 260 using openings 257 a of thecircuit pattern 257α as conformal masks.

Whereas in the second embodiment described above, chip capacitors 220are accommodated in the core substrate 230 alone, in the firstmodification, chip capacitors 320 each having a large capacity aremounted on the front surface and back surface of the core substrate 230,on top of the chip capacitors 220 accommodated in the core substrate230.

The IC chip conducts a complicated calculation, and in the calculationprocessing, it instantaneously consumes a large electric power. In orderto provide a large electric power to the IC chip, in this modification,chip capacitors 420 for power supply and chip capacitors 520 areprovided to the printed circuit board. The effect of providing the chipcapacitors 420 and 520 is the same as that attained in the fourthmodification of the first embodiment, and therefore, its descriptionwill be omitted.

Second Modification of Second Embodiment

A printed circuit board according to a second modification of the secondembodiment will be described with reference to FIG. 32. The printedcircuit board according to the second modification has the similarstructure as of the second embodiment described above, except for thefollowing points. That is, in the printed circuit board according to thesecond modification, the first electrode 221 and the second electrode222 of the chip capacitor 220 are directly connected to each otherthrough pads 292P1, 292P2 for power supply of the IC chip 290, and abump 276. In the second modification, the distance between the IC chipand each chip capacitor can be further shortened.

Third Modification of Second Embodiment

A printed circuit board according to a third modification of the secondembodiment will be described with reference to FIG. 33. The printedcircuit board according to the third modification has the similarstructure as of the second embodiment, except for the following points.That is, in the printed circuit board according to the thirdmodification, the first electrode 221, the second electrode 222 of thecapacitor 220 are directly connected to the through hole 246 by acircuit pattern 257α provided between the accommodation layer 230 a andthe connection layer 240. In the third modification, the wire lengthfrom the first electrode 221 and the second electrode 222 to thedaughter board can be shortened.

Fourth Modification of Second Embodiment

A printed circuit board according to a fourth modification of the secondembodiment will be described with reference to FIG. 18.

The printed circuit board according to the fourth modification has thesimilar structure as of the first modification described above, exceptfor the chip capacitors 20 accommodated in the core substrate 30. FIG.18 is a plan view showing the chip capacitor. FIG. 18(A) is a diagramshowing a chip capacitor before being cut from which a plurality ofpieces are to be obtained by cutting. In FIG. 18(A), a chain line showsthe cutting line. In the printed circuit board described in the firstembodiment, as shown in the plan view of FIG. 18(B), the firstelectrodes 21 and the second electrodes 22 are provide along the sideends of the chip capacitor. FIG. 18(C) is a diagram showing a chipcapacitor before being cut from which a plurality of pieces are to beobtained by cutting according to the fourth modification. In FIG. 18(C),a chain line shows the cutting line. In the printed circuit boarddescribed in the fourth modification, as shown in the plan view of FIG.18(D), the first electrodes 21 and the second electrodes 22 are providedinside the side ends of the chip capacitor.

In printed circuit board of the fourth modification, the chip capacitor20 in which the electrodes are formed along an inside of the outer edgethereof is used. Therefore, a chip capacitor having a large capacity canbe used as the chip capacitor 20.

A printed circuit board according to first alternative example of thefourth modification will be described referring to FIG. 19.

FIG. 19 is a diagram showing a plan view of the chip capacitor 20 to beaccommodated in the core substrate of the printed circuit boardaccording to a first alternative example. In the above-described firstembodiment, a plurality of chip capacitors each having a small capacityare accommodated in the core substrate. Contrary to this, in the firstalternative example, a large chip capacitor 20 having a large capacityis accommodated in the core substrate. The chip capacitor 20 includesfirst electrodes 21, second electrodes 22, a dielectric body 23, a firstconductive firm 24 connected to the first electrodes 21, a secondconductive film 25 connected to the second electrodes 22, and electrodes27 which are not connected to the first conductive film 24 and thesecond conductive film 25 and used for connecting the upper and lowersurfaces of the chip capacitor. The chip capacitor is connected to theIC chip and the daughter board through the electrodes 27.

In the printed circuit board according to the first alternative example,the chip capacitor 20 having a large size is used. Therefore, a chipcapacitor having a large capacity can be employed as the chip capacitor20. In addition, the use of large-sized chip capacitor 20 prevents thewarpage of the printed circuit board even if the printed circuit boardis repeatedly subjected to heat cycle.

Next, a printed circuit board according to a second alternative examplewill be described referring to FIG. 20. FIG. 20(A) is a diagram showinga chip capacitor before being cut from which a plurality of pieces areto be obtained by cutting. In FIG. 20(A), a chain line shows the cuttingline. FIG. 20(B) is a diagram showing a plan view of the chip capacitor.In the second alternative example, as shown in FIG. 20(B), a pluralityof chip capacitors from each of which a plurality of pieces are to beobtained by cutting (in FIG. 20(B), three pieces) are connected into onepiece unit having a large size.

In the second alternative example, the chip capacitor 20 having a largesize is used. Therefore, a chip capacitor having a large capacity can beemployed as the chip capacitor 20. In addition, the use of large-sizedchip capacitor 20 prevents the warpage of the printed circuit board evenif the printed circuit board is repeatedly subjected to heat cycle.

In the above-described embodiment, the chip capacitors are incorporatedin the printed circuit board. Instead of the chip capacitor, it is alsopossible to use a plate-like capacitor in which a conductive film isformed on a ceramic plate.

As to the printed circuit board of the second embodiment, the inductanceof the chip capacitor 220 embedded in the core substrate, and theinductance of the chip capacitor mounted on the back surface of theprinted circuit board (on the surface at the side of daughter board) areshown as follows.

In the case of a single capacitor:

A capacitor of embedded type: 137 pH

A capacitor of back surface mounted type: 287 pH

In the case of eight capacitors connected in parallel:

Capacitors of embedded type: 60 pH

Capacitors of back surface mounted type: 72 pH

In both cases where a single capacitor is used and where a plurality ofcapacitors are connected in parallel to obtain an increased capacity, aninductance can be lowered by incorporating the chip capacitor.

Hereinafter, the results of reliability test will be described. In thetest, the rate of change in the electrostatic capacity of a single chipcapacitor in the printed circuit board of the second embodiment wasmeasured.

Rate of change in electrostatic capacity (measured at a frequency of 100Hz) (measured at a frequency of 1 kHz)

Steam 168 hours: 0.3% 0.4% HAST 100 hours: −0.9% −0.9% TS 1000 cycles:1.1% 1.3%

In the Steam test, the chip capacitor was subjected to steam to be keptat a moisture of 100%. In the HAST test, the chip capacitor was left for100 hours at a relative moisture of 100%, an applied voltage of 1.3V,and at a temperature of 121° C. In the TS test, the chip capacitor waslest for 30 minutes at −125° C., and 30 minutes for 55° C., and thistest was repeated 1000 times.

In the above-described reliability test, it was realized that theprinted circuit board incorporating the chip capacitor attains areliability of the same level as the conventional printed capacitor onwhich a capacitor is mounted on its surface. As described above, in theTS test, even if an internal stress is generated due to the differencein the thermal expansion coefficients between the capacitor 220 made ofceramic, and the core substrate 230 and the connection layer 240 made ofresin, no problems are created such as a peeling of the chip capacitor220 from the connection layer 240, and the cracks in the core substrate230 and the connection layer 240. In this manner, high reliability canbe attained over a long period of time.

According to the structure of the second embodiment, there is no problemof lowering the electric characteristics caused by inductance.

Since the resin is charged in the space between the core substrate andthe capacitor, even if the stress is generated caused by the capacitors,the stress can be alleviated. In addition, no migration is created. As aresult, neither peeling nor dissolution is caused between the electrodesof the capacitor and the connecting sections of the via holes. Due tothese arrangements, the desired performance can be maintained in thereliability test.

In the case where the capacitors are coated with copper, the generationof migration can be prevented.

Third Embodiment

First, the structure of a printed circuit board according to a thirdembodiment of the present invention will be described with reference toFIGS. 37 and 38. FIG. 37 is a diagram showing a cross-section of aprinted circuit board 410. FIG. 38 is a diagram showing the state wherean IC chip 490 is mounted on the printed circuit board 410 shown in FIG.37, and the printed circuit board 410 is attached to a daughter board494.

As shown in FIG. 37, the printed circuit board 410 incorporates chipcapacitors 420, a core substrate 430 for accommodating chip capacitors420, and an interlayer resin insulating layer 450 constituting thebuildup layers 480A, 480B. The core substrate 430 is constituted by anaccommodating layer 430 a for accommodating the capacitors 420, and aconnection layer 440. Via holes 460 and a conductor circuit 458 areformed in the connection layer 440. Via holes 560 and a conductorcircuit 558 are formed in the interlayer resin insulating layer 450. Inthis embodiment, the buildup layer is constitute by a single interlayerresin insulating layer 450. As an alternative to this, the buildup layermay be constituted by a plurality of interlayer resin insulating layers.

As shown in FIG. 45, the chip capacitor 420 is constituted by a firstelectrode 421, a second electrode 422, and an dielectric body 423interposed between the first and second electrodes. The dielectric body423 includes a plurality of first conductive film 424 connected to thefirst electrode 421 and a plurality of second conductive film 425connected to the second electrode 422 in an opposed relation to eachother. In this embodiment, a connection for the first electrode 421 andthe second electrode 422 is established by forming via holes 460 made ofplating. As shown in FIG. 45, a metal (i.e. copper) layer 426 is exposedfrom the upper coating layer 428 formed on the first electrode 421 andthe second electrode 422. With this arrangement, as shown in FIG. 37,the connection with the via holes 460 made of copper plating isenhanced, and the connection resistance can be lowered.

As shown in FIG. 38, the via holes 560 in the upper buildup layer 480Aare formed with bumps 476 to be respectively connected to pads 492S1,492S2, 492P1, 492P2 of the IC chip 490. On the other hand, the via holes560 in the lower buildup layer 480B are formed with bump 476 to berespectively connected to pads 495S1, 495S2, 495P1, 495P2. Through holes446 are formed in the core substrate 430.

The pad 492S2 for signal of the IC chip 490 is connected to the pad495S2 for signal of the daughter board 494 through the bump 476-theconductor circuit 558-the via hole 560-the through hole 446-the via hole560-the bump 476. On the other hand, the pad 492S1 for signal of the ICchip 490 is connected to the pad 495S1 for signal of the daughter board494 through the bump 476-the via hole 560-the through hole 446-the viahole 560-the bump 476.

The pad 492P1 for power supply of the IC chip 490 is connected to thefirst electrode 421 of the chip capacitor 420 through the bump 476-viahole 560-the conductor circuit 458-the via hole 460. On the other hand,the pad 495P1 for power supply of the daughter board 494 is connected tothe first electrode 421 of the chip capacitor 420 through the bump476-the via hole 560-the through hole 446-the conductor circuit 458-thevia hole 460.

The pad 492P2 for power supply of the IC chip 490 is connected to thesecond electrode 422 of the chip capacitor 420 through the bump 476-thevia hole 560-the conductor circuit 458-the via hole 460. On the otherhand, the pad 495P2 for power supply of the daughter board 494 isconnected to the second electrode 422 of the chip capacitor 420 throughthe bump 476-the via hole 560-the through hole 446-the conductor circuit458-the via hole 460.

In the printed circuit board 410 of the third embodiment, the chipcapacitors 420 are placed immediately below the IC chip 490. Thedistance from the IC chip to each capacitor is shortened, and therefore,electric power can be instantaneously supplied to the IC chip. That is,the loop length which determines the loop inductance can be shortened.

In addition, the through hole 446 is formed between the chip capacitors420, and no signal line passes through the chip capacitors 420. In thisstructure, there is no problem that the impedance becomes discontinuousby the high dielectric body to generate a reflection, and that thetransmission is delayed by passing through the high dielectric body.

The external substrate (i.e. daughter board) 494 to be connected to theback surface of the printed circuit board is connected to the firstelectrode 421 and the second electrode 422 of the capacitor 420 throughthe via holes 460 formed in the connection layer 440 on the side of ICchip and the through holes 446 formed in the core substrate 430. Thatis, although the accommodation layer 430 a having a core material ishard to process, penetrating openings are formed in the accommodationlayer 430 a so that the terminal of the capacitor is not directlyconnected to the external substrate. As a result, the reliability of theconnection can be increased.

In this embodiment, as shown in FIG. 37, an adhesive 436 is interposedbetween the lower surface of the penetrating opening 437 of the coresubstrate 430 and the chip capacitor 420. In addition, a resin fillingagent 436 a is charged in a space between the side surface of thepenetrating opening 437 and the chip capacitor 420. The thermalexpansion coefficients of the resin layer 436 and the adhesive material436 a provided on the bottom surface of the chip capacitor 420 are setto the values lower than those of the core substrate 430 and theconnection layer 440, that is, are set to the values close to that ofthe chip capacitor 420 made of ceramics. In this manner, even ifinternal stress is generated between the core substrate 430 and theconnection layer 440, and the chip capacitor 420 caused by thedifference in the thermal expansion coefficients therebetween, cracksand peelings do not easily occur in the core substrate and theconnection layer 440. As a result, high reliability can be attained. Inaddition, the generation of migration can be prevented.

The process of manufacturing the printed circuit board of the thirdembodiment will be described with reference to FIGS. 34 to 37.

(1) Four prepregs 435 each having a core material impregnated with anepoxy resin are laminated on top of each other to form a laminated plate432 a, and penetrating openings 437 for accommodating chip capacitorsare formed in the laminated plate 432 a. On the other hand, two prepregs435 are laminated on top of each other to form a laminated plate 432 b(FIG. 34(A)). Instead of the epoxy resin, the prepreg 435 may beimpregnated with BT, phenolic resin, or reinforcement material such asglass cloth. The laminated plate 432 a and the laminated plate 432 b arelaminated to each other to form an accommodation layer 430 a. Then, asdescribed above referring to FIG. 45(A), chip capacitors 420 in which acoating layer 428 is peeled from the first and second electrodes 421,422 are accommodated in the penetrating opening 437 (FIG. 34(B)). It ispreferable that an adhesive 436 is interposed between the penetratingopening 437 and the chip capacitor 420. The resin and interlayer resininsulating layer used in this invention has melting points of 300° C. orlower. Therefore, when heat higher than 350° C. is applied, the resinand interlayer resin insulating layer may be dissolved, softened, orcarbonized. As the adhesive 436, it is preferable to use an adhesivehaving a thermal expansion coefficient smaller than that of the coresubstrate.

It is impossible to use substrates made of ceramic and AIN as the coresubstrate. These substrates are poor in outer shape processingcharacteristics, and cannot accommodate capacitors in some cases,because a space is created inside the substrate even if it is filledwith a resin.

(2) The resin film 440 a (i.e. a connection layer) is laminated on bothsides of the accommodating layer constituted by the laminated plate 432a and the laminated plate 432 b and accommodating the chip capacitors420 (FIG. 34(C)), and are pressed from both sides to flatten thesurface. Then, the resultant is heated and cured to form a coresubstrate 430 constituted by the accommodating layer 430 a accommodatingthe chip capacitors 420 and the connection layer 440 (FIG. 34(D)). Inthis embodiment, the accommodation layer 430 a which accommodates thecapacitors 420 and the connection layer 440 are bonded to each other byapplication of pressure from both sides to form the core substrate 430.As a result, the core substrate 430 has a flat surface. The interlayerresin insulating layer 450 and the conductor circuit 458 can belaminated in a later step in such a manner that high reliability isattained.

It is preferable that a resin filler 436 a is charged in the sidesurface of the penetrating openings 437 of the core substrate toincrease the air tightness. As the resin filler 436 a, it is preferableto use a filler having a thermal expansion coefficient smaller than thatof the core substrate. In this embodiment, the resin film 440 a may be aresin film of the same type as that used in the first embodiment whichhas no metal layer. As an alternative to this, a resin film (RCC) havinga metal layer on its one side may be used. That is, it is possible touse a both-sided plate, a one-sided plate, a resin plate having no metalfilm, and a resin film.

(3) Penetrating openings 446 each having a diameter of 300 to 500 μm forthrough holes are formed in the core substrate and the interlayer resininsulating layer 450 with a drill (FIG. 35(A)). Non-penetrating openings448 extending to the first electrode 421 and the second electrode 422 ofthe chip capacitor 420 are formed in the upper interlayer resininsulating layer 450 by CO₂ laser, YAG laser, excimer laser, or UV laser(FIG. 35(B)). As the case may be, an area mask on which penetratingopenings are formed at positions corresponding to the positions of thenon-penetrating openings is mounted, and an area processing is conductedby a laser. In the case where it is desired to form via holes havingdifferent sizes and diameter from each other, the lasers may be used incombination to form the via holes.

(4) A desmear process is performed. Subsequently, a palladium catalystis provided to the surface of the substrate 430, and then, the coresubstrate 430 is immersed into an electroless plating solution touniformly precipitate the electroless plated film 452 (FIG. 35(C)). As aresult of this, a rough layer can be formed on the surface of theelectroless copper plated film 452. The rough surface has Ra (meanroughness height) of 0.01 to 5 μm, and especially preferable is Ra of0.5 to 3 μm.

(6) A photosensitive dry film is attached on the surface of theelectroless plated film 452, and a mask is mounted thereon. Exposure tolight and development are performed to form a resist 454 having apredetermined pattern (FIG. 36(A)). In this embodiment, an electrolessplating is employed. Alternatively, a metal film of copper, nickel andthe like may be formed by sputtering. The sputtering is disadvantageousfrom the viewpoint of cost, but is advantageous in that the adhesionwith the resin can be improved. The core substrate 430 is immersed in anelectrolytic plating solution, and a current is allowed to flow in thecore substrate 430 through the electroless plated film 452 toprecipitate an electrolytic copper plated film 456 (FIG. 36(B)). Theresist 454 is peeled by 5% KOH, and the electroless plated film 452located under the resist 454 is etched and removed with a mixed solutionof sulfuric acid and hydrogen peroxide. As a result, via holes 460 areformed in the non-penetrating openings 448 of the connection layer 440,a conductor circuit 458 is formed on the surface of the connection layer440, and through holes 446 are formed in the penetrating openings 446 aof the core substrate 430 (FIG. 36(C)). The subsequent processes are thesame as the steps (10) to (15) of the second embodiment which has beendescribed above, and therefore, their description will be omitted.

The processes of mounting the IC chip on the printed circuit board, andattaching the printed circuit board to the daughter board are the sameas those of the first embodiment, and their description will be omitted.

First Modification of Third Embodiment

A printed circuit board according to a first modification of the thirdembodiment will be described with reference to FIG. 39. The printedcircuit board according to the first modification has the similarstructure as of the first modification described above, except for thefollowing points. That is, in the printed circuit board of the firstmodification, conductive pins 496 are provided, and a connection withthe daughter board is established through the conductive pins 496.

Whereas in the third embodiment described above, chip capacitors 420 areaccommodated in the core substrate 430 alone, in the first modification,chip capacitors 520 each having a large capacity are mounted on thefront surface and back surface of the core substrate 430, on top of thechip capacitors 420 accommodated in the core substrate 430.

The IC chip conducts a complicated calculation, and in the calculationprocessing, it instantaneously consumes a large electric power. In orderto provide a large electric power to the IC chip, in the firstmodification, chip capacitors 420 for power supply and chip capacitors520 are provided to the printed circuit board. The effect of providingthe chip capacitors 420 and 520 is the same as that attained in thefourth modification of the first embodiment, and therefore, itsdescription will be omitted.

Second Modification of Third Embodiment

A printed circuit board according to a second modification of the thirdembodiment will be described with reference to FIG. 42. The printedcircuit board according to the second modification has the similarstructure as of the third modification described above, except for thefollowing points. In the third embodiment, the core substrate 430 isconstituted by the accommodation layer 430 a having connection layers440 on its both sides. Contrary to this, in the second embodiment, theconnection layer 440 is formed only on the upper surface of theaccommodation layer 430 a.

The processes of manufacturing the printed circuit board according tothe second modification of the third embodiment will be described withreference to FIGS. 39 to 41.

(1) Four prepregs 435 impregnated with an epoxy resin are laminated ontop of each other to form a laminated plate 432 a, and penetratingopenings 437 for accommodating chip capacitors are formed in thelaminated plate 432 a. On the other hand, two prepregs 435 are laminatedon top of each other to form a laminated plate 432 b (FIG. 40(A)). Chipcapacitors 420 are mounted through the adhesives 436 on the laminatedplate 432 b at positions corresponding to the penetrating openings ofthe laminated plate 432 a (FIG. 40(B)). The laminated plate 432 a andthe laminated plate 432 b are laminated to each other to form anaccommodating layer 430 a accommodating the chip capacitors 420 (FIG.40(C)).

(2) The resin film 440 a (i.e. a connection layer) is laminated on theaccommodating layer constituted by the laminated plate 432 a and thelaminated plate 432 b, and accommodating the chip capacitors 420 (FIG.40(D)), and the resultant is pressed from both sides to flatten thesurface. Then, heating and curing is conducted to form a core substrate430 constituted by the accommodating layer 430 a accommodating the chipcapacitors 420 and the connection layer 440 (FIG. 41(A)). In thisembodiment, the accommodation layer 430 a which accommodates thecapacitors 420 and the connection layer 440 are bonded to each other byapplication of pressure from both sides to form the core substrate 430.As a result, the core substrate 430 has a flat surface. The interlayerresin insulating layer 450 and the conductor circuit 558 can belaminated in such a manner that high reliability is attained.

(3) Penetrating openings 446 each having a diameter of 300 to 500 μm forthrough holes are formed in the core substrate and the interlayer resininsulating layer 450 with a drill (FIG. 41(B)). Non-penetrating openings448 extending to the first electrode 421 and the second electrode 422are formed in the upper interlayer resin insulating layer 450 by CO₂laser, YAG laser, excimer laser, or UV laser (FIG. 41(C)). Thesubsequent processes are the same as the steps (3) and after of thethird embodiment, and therefore, their description will be omitted.

Third Modification of Third Embodiment

A printed circuit board according to third modification of the thirdembodiment will be described with reference to FIG. 44. The printedcircuit board according to the third modification has the similarstructure as of the second modification of the third embodimentdescribed above, except for the following points. That is, in theprinted circuit board according to the second modification, via holes460 are formed on only one surface of the core substrate 430 on the ICchip side. Contrary to this, in the third modification, via holes 460are formed on both surfaces of the core substrate on the sides of ICchip and daughter board.

In the third modification, the via holes 460 are formed not only on thefront surface but also on the back surface. In this manner, the wirelength between the chip capacitors 420 and the daughter board can beshortened.

The processes of manufacturing the printed circuit board according tothe third modification of the third embodiment will be described withreference to FIG. 43.

(1) Four prepregs 435 impregnated with an epoxy resin are laminated ontop of each other to form a laminated plate 432 a, and penetratingopenings 437 for accommodating chip capacitors are formed in thelaminated plate 432 a. On the other hand, two prepregs 435 are laminatedon top of each other to form a laminated plate 432 b, and penetratingopenings 439 extending to the electrodes are formed at positions wherethe chip capacitors are to be mounted (FIG. 43(A)). Chip capacitors 420are mounted on the laminated plate 432 b through the adhesive material436 at positions corresponding to the penetrating openings formed in thelaminated plate 432 a (FIG. 43(B)). The laminated plate 432 a and thelaminated plate 432 b are laminated to each other to form anaccommodating layer 430 a (FIG. 43(C)).

(2) The resin film 440 a (i.e. a connection layer) is laminated on theupper surface of the accommodating layer 430 a (FIG. 43(D)), and arepressed from both sides to flatten the surface. Then, the resultant isheated and cured to form a core substrate 430 constituted by theaccommodating layer 430 a accommodating the chip capacitors 420 and theconnection layer 440 (FIG. 44). The subsequent processes are the same asthe steps (3) and after of the third embodiment, and therefore, theirdescription will be omitted.

Fourth Modification of Third Embodiment

A printed circuit according to fourth modification of the thirdembodiment will be described referring to FIGS. 46 and 47.

The printed circuit board according to the fourth modification has thesimilar structure as of the third embodiment described above referringto FIG. 37, except for the following points. That is, in the printedcircuit board according to the fourth modification, as shown in FIG. 47,in the chip capacitor 420, the coating layer 428 (FIG. 45(A)) iscompletely peeled from the first and second electrodes 421, 422, andthen, the first and second electrodes are coated with a copper platedfilm 429. An electric connection for the first and second electrodes421, 422 coated with the copper plated film 429 is established throughvia holes 460 constituted by a copper plating. The electrodes 421, 422of the chip capacitor are metallized and has pits and projections ontheir surfaces. If the metal layer 426 is left uncoated and exposed tothe outside, the resin may be left in the pits and projections in thestep of forming non-penetrating openings 448 in the connection layer440. The resin left in the pits and projections may cause adisconnection between the first and second electrodes 421, 422 and thevia hole 460. Contrary to this, in the fourth modification, the surfacesof the first and second electrodes 421, 422 coated with the copperplated film 429 are flat and smooth. When the non-penetrating openings448 are formed in the connection layer 440 formed on the electrodes, noresin is left on the surfaces of the electrodes. When the via holes 460are formed, the connection between the via holes 460 and the electrodes421, 422 has increased reliability.

Since the via holes 460 are made by plating into the electrodes 421, 422formed with the copper plated film 429, the electrodes 421, 422 arefirmly connected to the via holes 460. No disconnection occurs betweenthe electrodes 421, 422 and via holes 460 even when a heat cycle test isconducted. No migration is generated, and in addition, no problem arisesat the connection in the via holes of the capacitor.

The copper plated film 429 is formed after a nickel/tin layer (i.e.coating layer) provided onto the surface of the metal layer 426 in thestep of manufacturing the chip capacitor is peeled off at the time ofmounting the chip capacitor onto the printed circuit board.Alternatively, the copper plated film 429 may be directly provided ontothe surface of the metal layer 426 in the step of manufacturing the chipcapacitor 420. In the fourth modification, as is the case of the thirdembodiment, openings which extend to the copper plated film 429 of theelectrodes are formed by a laser, and then a desmear process isperformed to form via holes by copper plating. Therefore, even if anoxide film is formed on the surface of the copper plated film 429, theoxide film can be removed in the laser or desmear process.

On the surface of the dielectric body 423 made of ceramic of the chipcapacitor 420, a rough surface 423α is formed. The rough surface 423αcontributes to an increased adhesion between the chip capacitor 420 madeof ceramic and the connection layer 440 made of resin, thereby avoidingthe connection layer 440 from peeling from the interface with the chipcapacitor 420 even when a heat cycle test is conducted. The roughsurface 423 α can be formed by polishing the surface of the chipcapacitor 420 after the sintering step, or by roughening the surface ofthe chip capacitor 420 before the sintering step. In the fourthmodification, the surface of the chip capacitor is roughened to increaseits adhesion with the resin. Alternatively, the surface of the chipcapacitor may be subjected to silane coupling process.

In the above-described embodiment, the chip capacitors are incorporatedin the printed circuit board. Instead of the chip capacitor, it is alsopossible to use a plate-like capacitor in which a conductive film isformed on a ceramic plate. Needless to say, the structure in which thecopper plating is provided and the structure in which the surface of thechip capacitor is roughened as employed in the fourth modification maybe applicable to the third embodiment, the first, second, and thirdmodifications of the third embodiment.

Fifth Modification of Third Embodiment

The structure of a printed circuit board according to a fifthmodification of the third embodiment will be described with reference toFIG. 18.

The printed circuit board according to the fifth modification has thesimilar structure as of the first modification described above, exceptfor the chip capacitors 20 accommodated in the core substrate 30. FIG.18 is a plan view showing the chip capacitor. FIG. 18(A) is a diagramshowing a chip capacitor before being cut from which a plurality ofpieces are to be obtained by cutting. In FIG. 18(A), a chain line showsthe cutting line. In the printed circuit board described in the firstembodiment, as shown in the plan view of FIG. 18(B), the firstelectrodes 21 and the second electrodes 22 are provide along the sideends of the chip capacitor. FIG. 18(C) is a diagram showing a chipcapacitor before being cut from which a plurality of pieces are to beobtained by cutting according to the fifth modification. In FIG. 18(C),a chain line shows the cutting line. In the printed circuit boarddescribed in the fifth modification, as shown in the plan view of FIG.18(D), the first electrodes 21 and the second electrodes 22 are providedinside the side ends of the chip capacitor.

In the fifth modification, the printed circuit board has a chipcapacitor 20 in which the electrodes are formed inside the side endsthereof. Therefore, a chip capacitor having a large capacity can be usedas the chip capacitor 20.

A printed circuit board according to first alternative example of thefifth modification will be described referring to FIG. 19.

FIG. 19 is a diagram showing a plan view of the chip capacitor 20 to beaccommodated in the core substrate of the printed circuit boardaccording to a first alternative example. In the above-described firstembodiment, a plurality of chip capacitors each having a small capacityare accommodated in the core substrate. Contrary to this, in the firstalternative example, a large chip capacitor 20 having a large capacityis accommodated in the core substrate. The chip capacitor 20 includesfirst electrodes 21, second electrodes 22, a dielectric body 23, a firstconductive firm 24 connected to the first electrodes 21, a secondconductive film 25 connected to the second electrodes 22, and electrodes27 which are not connected to the first conductive film 24 and thesecond conductive film 25 and used for connecting the upper and lowersurfaces of the chip capacitor. The chip capacitor is connected to theIC chip and the daughter board through the electrodes 27.

In the printed circuit board according to the first alternative example,the chip capacitor 20 having a large size is used. Therefore, a chipcapacitor having a large capacity can be employed as the chip capacitor20. In addition, the use of large-sized chip capacitor 20 prevents thewarpage of the printed circuit board even if the printed circuit boardis repeatedly subjected to heat cycle.

Next, a printed circuit board according to a second alternative examplewill be described referring to FIG. 20. FIG. 20(A) is a diagram showinga chip capacitor before being cut from which a plurality of pieces areto be obtained by cutting. In FIG. 20(A), a chain line shows the cuttingline. FIG. 20(B) is a diagram showing a plan view of the chip capacitor.In the second alternative example, as shown in FIG. 20(B), a pluralityof chip capacitors from each of which a plurality of pieces are to beobtained by cutting (in FIG. 20(B), three pieces) are connected into onepiece unit having a large size.

In the second alternative example, the chip capacitor 20 having a largesize is used. Therefore, a chip capacitor having a large capacity can beemployed as the chip capacitor 20. In addition, the use of large-sizedchip capacitor 20 prevents the warpage of the printed circuit board evenif the printed circuit board is repeatedly subjected to heat cycle.

In the above-described embodiment, the chip capacitors are incorporatedin the printed circuit board. Instead of the chip capacitor, it is alsopossible to use a plate-like capacitor in which a conductive film isformed on a ceramic plate.

As to the printed circuit board of the fourth modification of the thirdembodiment, the inductance of the chip capacitor 420 embedded in thecore substrate, and the inductance of the chip capacitor mounted on theback surface of the printed circuit board (on the surface at the side ofdaughter board) are shown as follows.

In the case of a single capacitor:

A capacitor of embedded type: 137 pH

A capacitor of back surface mounted type: 287 pH

In the case of eight capacitors connected in parallel:

Capacitors of embedded type: 60 pH

Capacitors of back surface mounted type: 72 pH

In both cases where a single capacitor is used and where a plurality ofcapacitors are connected in parallel to obtain an increased capacity, aninductance can be lowered by incorporating the chip capacitor.

Hereinafter, the results of reliability test will be described. In thetest, the rate of change in the electrostatic capacity of a single chipcapacitor in the printed circuit board of the first embodiment wasmeasured.

Rate of change in electrostatic capacity (measured at a frequency of 100Hz) (measured at a frequency of 1 kHz)

Steam 168 hours: 0.3% 0.4% HAST 100 hours: −0.9% −0.9% TS 1000 cycles:1.1% 1.3%

In the Steam test, the chip capacitor was subjected to steam to be keptat a moisture of 100%. In the HAST test, the chip capacitor was left for100 hours at a relative moisture of 100%, an applied voltage of 1.3V,and at a temperature of 121° C. In the TS test, the chip capacitor waslest for 30 minutes at −125° C., and 30 minutes for 55° C., and thistest was repeated 1000 times.

In the above-described reliability test, it was realized that theprinted circuit board incorporating the chip capacitor attains areliability of the same level as the conventional printed capacitor onwhich a capacitor is mounted on its surface. As described above, in theTS test, even if an internal stress is generated due to the differencein the thermal expansion coefficients between the capacitor made ofceramic, and the core substrate and the resin insulating layer made ofresin, no problems are created such as a disconnection between theterminal of the chip capacitor and the via holes, a peeling of the chipcapacitors from the resin insulating layer, and the cracks in the resininsulating layer. In this manner, high reliability can be attained overa long period of time.

According to the structure of the third embodiment, there is no problemof lowering the electric characteristics caused by inductance.

Since the resin is charged in the space between the core substrate andthe capacitors, even if the stress is generated caused by thecapacitors, the stress can be alleviated. In addition, no migration iscreated. As a result, neither peeling nor dissolution is caused betweenthe electrodes of the capacitors and the connecting sections of the viaholes. Due to these arrangements, the desired performance can bemaintained in the reliability test.

In the case where the electrodes of the capacitors are coated withcopper, the generation of migration can be prevented.

Fourth Embodiment

The structure of a printed circuit board according to a fourthembodiment of the present invention will be described with reference toFIGS. 51 and 52. FIG. 51 is a diagram showing a cross section of aprinted circuit board 610. FIG. 52 is a diagram showing the state wherean IC chip 690 is mounted on the printed circuit board 610 shown in FIG.51, and the printed circuit board 610 is attached to a daughter board694.

As shown in FIG. 51, the printed circuit board 610 incorporates chipcapacitors 620, a core substrate 630 for accommodating chip capacitors620, and an interlayer resin insulating layer 650 constituting thebuildup layers 680A, 680B. The core substrate 630 is constituted by anaccommodating layer 630 a for accommodating the capacitors 620, and aconnection layer 640. Via holes 660 and a conductor circuit 658 areformed in the connection layer 640. Via holes 760 and a conductorcircuit 758 are formed in the interlayer resin insulating layer 650. Inthis embodiment, the buildup layer is constitute by a single interlayerresin insulating layer 650. As an alternative to this, the buildup layermay be constituted by a plurality of interlayer resin insulating layers.

As shown in FIG. 45, the chip capacitor 620 is constituted by a firstelectrode 621, a second electrode 622, and a dielectric body 623interposed between the first and second electrodes 621, 622. Thedielectric body 623 includes a plurality of first conductive film 624connected to the first electrode 621 and a plurality of secondconductive film 625 connected to the second electrode 622 in an opposedrelation to each other.

As shown in FIG. 52, the via holes 760 in the upper buildup layer 680Aare formed with bumps 676 to be respectively connected to pads 692S1,692S2, 692 P1, 692P2 of the IC chip 690. On the other hand, the viaholes 760 in the lower buildup layer 680B are formed with bumps 676 tobe respectively connected to pads 695S1, 695S2, 695P1, 695P2. Throughholes 646 are formed in the core substrate 630.

The pad 692S2 for signal of the IC chip 690 is connected to the pad695S2 for signal of the daughter board 694 through the bump 676-theconductor circuit 758-the via hole 760-the through hole 646-and via hole760-the bump 676. On the other hand, the pad 692S1 for signal of the ICchip 690 is connected to the pad 695S1 for signal of the daughter board694 through the bump 676-the via hole 760-the through hole 646-via hole760-bump 676.

The pad 692P1 for power supply of the IC chip 690 is connected to thefirst electrode 621 of the chip capacitor 620 through the bump 676-viahole 760-the conductor circuit 658-the via hole 660. On the other hand,the pad 695P1 for power supply of the daughter board 694 is connected tothe first electrode 621 of the chip capacitor 620 through the bump676-the via hole 760 the conductor circuit 658 the via hole 660.

The pad 692P2 for power supply of the IC chip 690 is connected to thesecond electrode 622 of the chip capacitor 620 through the bump 676-thevia hole 760-the conductor circuit 658-the via hole 660. On the otherhand, the pad 695P2 for power supply of the daughter board 694 isconnected to the second electrode 622 of the chip capacitor 620 throughthe bump 676-the via hole 760-the conductor circuit 658-the via hole660.

In the printed circuit board 610 of the fourth embodiment, the chipcapacitors 620 are placed immediately below the IC chip 690. Thedistance from the IC chip to each capacitor is shortened, and therefore,electric power can be instantaneously supplied to the IC chip. That is,the loop length which determines the loop inductance can be shortened.

In addition, the through hole 646 is formed between the chip capacitors620, and no signal line passes through the chip capacitors 620. In thisstructure, there is no problem that the impedance becomes discontinuousby the high dielectric body to generate a reflection, and that thetransmission is delayed by passing through the high dielectric body.

The external substrate (i.e. daughter board) 694 to be connected to theback surface of the printed circuit board is connected to the firstelectrode 621 and the second electrode 622 of the capacitor 620 throughthe via holes 660 formed in the connection layer 640 on the side of ICchip and the via holes 660 formed in the connection layer 640 on theside of daughter board. That is, since the terminals 621, 622 aredirectly connected to the IC chips 690, and the daughter board 694, thewire length therebetween can be shortened.

In the fourth embodiment, an adhesive 636 is interposed between the sidesurface of the through opening 637 of the core substrate 630 and thechip capacitor 620. The thermal expansion coefficient of the adhesive636 is set to the value lower than those of the core substrate 630 andthe connection layer 640, that is, are set to the value close to that ofthe chip capacitor 620 made of ceramics. In this manner, even ifinternal stress is generated between the core substrate 630 and theconnection layer 640, and the chip capacitor 620 caused by thedifference in the thermal expansion coefficients therebetween, cracksand peelings do not easily occur in the core substrate and theconnection layer 640. As a result, high reliability can be attained. Inaddition, the generation of migration can be prevented.

Next, the method for manufacturing the printed circuit board describedabove referring to FIG. 51 will be described with reference to FIGS. 48to 49.

(1) Prepregs each having a core material impregnated with an epoxy resinare laminated on top of each other to form a laminated plate (i.e. anaccommodation layer) 632 a, and penetrating openings 637 foraccommodating chip capacitors are formed in the laminated plate 632 a(FIG. 48(A)). The prepreg 435 may be those generally used in printedcircuit board such as prepreg impregnated with, instead of the epoxyresin, BT, phenolic resin, or reinforcement material such as glasscloth. It is also possible to use a resin substrate having no corematerial such as glass cloth.

It is impossible, however, to use substrates made of ceramic and AIN asthe core substrate. These substrates are poor in outer shape processingcharacteristics, and cannot accommodate capacitors in some cases. Inaddition, a space is created inside the substrate even if it is filledwith a resin.

(2) The chip capacitors 620 are accommodated in the penetrating openings637 of the accommodation layer 632 a (FIG. 48(B)). In this case, it isdesirable to peel off the coating 626 from the surface of the first andsecond electrodes 621, 622 of the chip capacitors 620 in order toincrease the connection with the via holes 660 to be formed on the upperlayer. It is preferable to interpose an adhesive 636 between the throughopenings 637 and the chip capacitors 620. As the adhesive 636, it isdesirable to use an adhesive having a thermal expansion coefficientsmaller than those of the core substrate and connection layer.

(3) A resin film 640 a, the accommodation layer 632 a accommodating thechip capacitors 620, and another resin film 640 a are laminated on topof one another (FIG. 48(C)). The resin film 640 a may be made of, as isthe case of the first embodiment, thermosetting resin such as epoxy, BT,polyimide, and olefin, or mixtures of thermosetting resins andthermoplastic resins. In this embodiment, it is preferable to use a filmhaving no core material so that the penetrating openings can be easilyformed. In this embodiment, a resin film 640 a having no metal layer islaminated. As an alternative to this, a resin film (RCC) having a metallayer on its one side may be used. That is, it is possible to use aboth-sided plate, a one-sided plate, a resin plate having no metal film,and a resin film. It is preferable that a resin filler 636 a is chargedin the upper and lower surfaces of the chip capacitors 620 to increasethe air tightness. The resin and interlayer resin insulating layer usedin this invention have melting points of 300° C. or lower. Therefore,when heat higher than 350° C. is applied, the resin and interlayer resininsulating layer may be dissolved, softened, or carbonized.

(4) The accommodation layer 632 a and the resin films 640 a laminated ontop of one another are pressed from both sides to flatten the surface.Then, heating and curing is performed to form a core substrate 630constituted by an accommodation layer 630 a accommodating the chipcapacitors 620 and a connection layer 640 (FIG. 49(A)). In thisembodiment, the accommodation layer 630 a which accommodates thecapacitors 620 and the connection layer 640 are bonded to each other byapplication of pressure from both sides to form a core substrate 630. Asa result, the core substrate 630 has a flat surface. The interlayerresin insulating layer 650 and the conductor circuit 758 can belaminated in a later step in such a manner that high reliability isattained.

(5) Non-penetrating openings 648 to be via holes are formed in the upperconnection layer 640 by CO₂ laser, YAG laser, excimer laser, or UV laser(FIG. 49(B)). As the case may be, an area mask on which penetratingopenings are formed at positions corresponding to the positions of thenon-penetrating openings is mounted, and an area processing is conductedby a laser. In the case where it is desired to form via holes havingdifferent sizes and diameter from each other, the lasers may be used incombination to form the via holes.

(6) If necessary, smear in the via holes may be conducted by a gasplasma treatment using a gaseous matter such as oxygen and nitrogen, ordry treatment such as corona treatment, or by immersion into an oxidizersuch as permagnetic acid. Subsequently, penetrating openings 646 a eachhaving a diameter of 50 to 500 μm for through holes are penetrated inthe core substrate 630 constituted by the connection layer 640, theaccommodation layer 630 a, and the connection layer 640 by a drill or alaser (FIG. 49(C)).

(7) A metal film is formed on the surface layer of the connection layer640, the non-penetrating openings 648 for via holes, and the penetratingopenings 646 a for through holes of the core substrate 630. For thispurpose, a palladium catalyst is provided on the surface of theconnection layer 640, and then, the core substrate 630 is immersed in anelectroless plating solution to uniformly precipitate an electrolesscopper plated film 652 (FIG. 50(A)). In this embodiment, an electrolessplating is employed. Alternatively, a metal film of copper, nickel andthe like may be formed by sputtering. The sputtering is disadvantageousfrom the viewpoint of cost, but is advantageous in that the adhesionwith the resin film can be improved. As the case may be an electrolessplated film may be formed after the metal layer is formed by sputtering.Depending on the kind of resin, there are cases where the catalystcannot be stably provided thereto. In this case, the electroless platedfilm is effective in stably providing the catalyst to such a resin. Inaddition, the electrolytic plating is more stably precipitated in thecase of forming the electroless plated film. The metal film 652 ispreferably formed into the thickness of 0.1 to 3 mm.

(8) A photosensitive dry film is attached to the surface of the metalfilm 652, and a mask is placed thereon. Exposure to light anddevelopment are performed to form a resist 654 having a predeterminedpattern. The core substrate 630 is immersed into an electrolytic platingsolution to allow a current to flow in the core substrate 630 throughthe electroless plated film 652 to precipitate an electrolytic copperplated film 656 (FIG. 50(B)). The resist 654 is peeled by 5% KOH, andthen, the electroless plated film 652 below the resist 654 is etched andremoved by a mixed solution of sulfuric acid and hydrogen peroxide. As aresult, via holes 660 and a conductor circuit 658 are formed in theconnection layer 640, and through holes 646 are formed in thepenetrating openings 646 a of the core substrate 630 (FIG. 50(C)). Thesubsequent processes are the same as the steps (10) to (15) of thesecond embodiment, and therefore, their description will be omitted.

The processes of mounting the IC chip on the printed circuit board, andattaching the printed circuit board to the daughter board are the sameas those of the first embodiment, and their description will be omitted.

First Modification of Fourth Embodiment

FIG. 53 is a diagram showing a printed circuit board according to afirst modification of the fourth embodiment. It is also possible, as isthe case of the first modification shown in FIG. 53, the first electrode621 and the second electrode 622 may be connected to the via holes 660via the adhesive material 634. The conductive adhesive material 634 maybe a material having both conductivity and adhesiveness such as a solder(Sn/Pb, Sn/Sb, Sn/Ag), conductive pastes, and resins impregnated withmetal particles.

Second Modification of Fourth Embodiment

A printed circuit board according to a second modification of the fourthembodiment will be described with reference to FIG. 54. The printedcircuit board according to a second modification has a similar structureas of the fourth embodiment, except for the following points. That is,in the printed circuit board of the second modification, conductivepints 696 are provided, and a connection with the daughter board isestablished through the conductive pins 696.

Whereas in the fourth embodiment described above, chip capacitors 220are accommodated in the core substrate 630 alone, in the firstmodification, chip capacitors 720 each having a large capacity aremounted on the front surface and back surface of the core substrate 630,on top of the chip capacitors 620 accommodated in the core substrate630.

The IC chip conducts a complicated calculation, and in the calculationprocessing, it instantaneously consumes a large electric power. In orderto provide a large electric power to the IC chip, in this modification,a chip capacitor 620 for power supply and a chip capacitor 720 areprovided to the printed circuit board. The effect of providing the chipcapacitors 620 and 720 is the same as that attained in the fourthmodification of the first embodiment, and therefore, its descriptionwill be omitted.

Third Modification of Fourth Embodiment

A printed circuit board according to a third modification of the presentinvention will be described with reference to FIG. 55. A printed circuitboard 610 to the third modification has the similar structure as of thefourth embodiment described above, except for the following points. Thatis, in the printed circuit board 610 according to the thirdmodification, filled vias 660 are formed on a first electrode 621 and asecond electrode 622 of chip capacitors 620. The chip capacitors 620 areconnected to the bumps 692 of the IC chips 690 through the filled vias760.

Fourth Modification of Fourth Embodiment

A printed circuit board according to a fourth modification of the fourthembodiment will be described with reference to FIG. 56. A printedcircuit board 610 according to the fourth modification has the similarstructure as of the fourth embodiment described above, except for thefollowing points. That is, in the printed circuit board according to thefourth modification, filled vias 660 are formed on a first electrode 621and a second electrode 622 of chip capacitors 620. The chip capacitors620 are connected to the bumps 692P1, 692P2 of the IC chips 690 throughthe filled vias 760 formed immediately above the filled vias 660. Withthis arrangement of the fourth modification, the distance between the ICchip and each chip capacitor can be shortened to the minimum value.

Fifth Modification of Fourth Embodiment

A printed circuit board according to a fifth modification of the presentinvention will be described with reference to FIG. 57. A printed circuitboard 610 according to the fifth modification has the similar structureas of the fourth embodiment described above, except for the followingpoints. That is, in the printed circuit board according to the fifthmodification, pads on the side of IC chip 690 and the pads 695 on theside of daughter board 694 are connected through a first electrode 621,and a first electrode 622 of the chip capacitors 620. In other words,through holes for power supply and through holes for ground of the ICchip and daughter board are omitted. With this arrangement of the fifthmodification, the wiring density can be increased as compared with thecase of fourth embodiment.

Sixth Modification of Fourth Embodiment

A printed circuit board according to a sixth modification of the fourthembodiment will be described with reference to FIGS. 58 and 59.

A printed circuit board according to the sixth modification has thesimilar structure as of the fourth embodiment described above referringto FIG. 51, except for the following points. That is, in the printedcircuit board according to the sixth modification, as shown in FIG. 59,in the chip capacitor 620, the coating layer 626 (see FIG. 45) iscompletely peeled from the first and second electrodes 621, 622, andthen, the first and second electrodes are coated with a copper platedfilm 629. An electric connection for the first and second electrodes621, 622 coated with the copper plated film 629 is established throughvia holes 660 constituted by copper plating. The electrodes 621, 622 ofthe chip capacitor are metallized and has pits and projections on theirsurfaces. If the metal layer is left uncoated and exposed to theoutside, the resin may be left in the pits and projections in the stepof forming non-penetrating openings 648 in the connection layer 640. Theresin left in the pits and projections may cause a disconnection betweenthe first and second electrodes 621, 622 and the via holes 660. Contraryto this, in the sixth modification, the surfaces of the first and secondelectrodes 621, 622 coated with the copper plated film 629 are flat andsmooth. When the non-penetrating openings 648 are formed in theconnection layer 640 formed on the electrodes, no resin is left on thesurfaces of the electrodes 621, 622. When the via holes 660 are formed,the connection between the via holes 660 and the electrodes 621, 622 hasincreased reliability.

Since the via holes 660 are made by plating into the electrodes 621, 622formed with the copper plated film 629, the electrodes 621, 622 arefirmly connected to the via holes 660. No disconnection occurs betweenthe electrodes 621, 622 and via holes 660 even when a heat cycle test isconducted.

The copper plated film 629 is formed after a nickel/tin layer (i.e. acoating layer) provided onto the surface of the metal layer 628constituting the first and first electrodes in the step of manufacturingthe chip capacitor is peeled off at the time of mounting the chipcapacitor onto the printed circuit board. Alternatively, the copperplated film 629 may be directly provided onto the surface of the metallayer 629 in the step of manufacturing the chip capacitor 620. In thesixth modification, as is the case of the fourth embodiment, openingswhich extend to the copper plated film 629 of the electrodes are formedby a laser, and then a desmear process is performed to form via holes bycopper plating. Therefore, even if an oxide film is formed on thesurface of the copper plated film 629, the oxide film can be removed inthe laser or desmear process. In this manner, the first and secondelectrodes 621, 622 can be properly connected to the via holes 660.

As is the case of the first embodiment, as shown in FIG. 17(B), thefirst electrodes 21, 22 of the capacitor 20 may be partially uncoatedwith the coating 28. When partially uncoated and exposed to the outside,the connection of the first and second electrodes 21, 22 to the viaholes 660 can be enhanced.

On the surface of the dielectric body 623 made of ceramic of the chipcapacitor 620, a rough surface 623α is formed. The rough surface 623αcontributes to an increased adhesion between the chip capacitor 620 madeof ceramic and the connection layer 640 made of resin, thereby avoidingthe connection layer 640 from peeling from the interface with the chipcapacitor 620 even when a heat cycle test is conducted. The roughsurface 623 α can be formed by polishing the surface of the chipcapacitor 620 after the sintering step, or by roughening the surface ofthe chip capacitor 620 before the sintering step. In the sixthmodification, the surface of the chip capacitor is roughened to increaseits adhesion with the resin. Alternatively, the surface of the chipcapacitor may be subjected to silane coupling process.

Seventh Modification of Fourth Embodiment

A structure of a printed circuit board according to a seventhmodification of the fourth embodiment will be described referring toFIG. 18.

The printed circuit board according to the seventh modification has thestructure similar to that of the first embodiment, except for thestructure of the chip capacitors 20 accommodated in the core substrate30. FIG. 18 is a plan view showing the chip capacitors. FIG. 18(A) is adiagram showing a chip capacitor before being cut from which a pluralityof pieces are to be obtained by cutting. In FIG. 18(A), a chain lineshows the cutting line. In the printed circuit board described in thefirst embodiment, as shown in the plan view of FIG. 18(B), the firstelectrodes 21 and the second electrodes 22 are provide along the sideends of the chip capacitor. FIG. 18(C) is a diagram showing a chipcapacitor before being cut from which a plurality of pieces are to beobtained by cutting according to the seventh modification. In FIG.18(C), a chain line shows the cutting line. In the printed circuit boarddescribed in the seventh modification, as shown in the plan view of FIG.18(D) the first electrodes 21 and the second electrodes 22 are provideinside the side ends of the chip capacitor.

In the printed circuit board of the seventh modification, a chipcapacitor 20 in which the electrodes are formed inside the side endsthereof is used. Therefore, a chip capacitor having a large capacity canbe used as the chip capacitor 20.

A printed circuit board according to a first alternative example of theseventh modification will be described referring to FIG. 19.

FIG. 19 is a diagram showing a plan view of the chip capacitor 20 to beaccommodated in the core substrate of the printed circuit boardaccording to the first alternative example. In the above-described firstembodiment, a plurality of chip capacitors each having a small capacityare accommodated in the core substrate. Contrary to this, in the firstalternative example, a large chip capacitor having a large capacity isaccommodated in the core substrate. The chip capacitor 20 includes firstelectrodes 21, second electrodes 22, a dielectric body 23, a firstconductive firm 24 connected to the first electrodes 21, a secondconductive film 25 connected to the second electrodes 22, and electrodes27 which are not connected to the first conductive film 24 and thesecond conductive film 25 and used for connecting the upper and lowersurfaces of the chip capacitor. The chip capacitor is connected to theIC chip and the daughter board through the electrodes 27.

In the printed circuit board according to the first alternative example,the chip capacitor 20 having a large size is used. Therefore, a chipcapacitor having a large capacity can be employed as the chip capacitor20. In addition, the use of large-sized chip capacitor 20 prevents thewarpage of the printed circuit board even if the printed circuit boardis repeatedly subjected to heat cycle.

Next, a printed circuit board according to a second alternative examplewill be described referring to FIG. 20. FIG. 20(A) is a diagram showinga chip capacitor before being cut from which a plurality of pieces areto be obtained by cutting. In FIG. 20(A), a chain line shows the cuttingline. FIG. 20(B) is a diagram showing a plan view of the chip capacitor.In the second alternative example, as shown in FIG. 20(B), a pluralityof chip capacitors from each of which a plurality of pieces are to beobtained by cutting (in FIG. 20(B), three pieces) are connected into onepiece unit having a large size.

In the second alternative example, the chip capacitor 20 has a largesize. Therefore, a chip capacitor having a large capacity can beemployed as the chip capacitor 20. In addition, the use of large-sizedchip capacitor 20 prevents the warpage of the printed circuit board evenif the printed circuit board is repeatedly subjected to heat cycle.

In the above-described embodiment, the chip capacitors are incorporatedin the printed circuit board. Instead of the chip capacitor, it is alsopossible to use a plate-like capacitor in which a conductive film isformed on a ceramic plate. Needless to say, the structure in which thecopper plating is provided and the structure in which the surface of thechip capacitor is roughened as employed in the sixth modification may beapplicable to the fourth embodiment, the first, second, third, fourth,fifth, and sixth modifications.

As to the printed circuit board according to the sixth modification ofthe fourth embodiment, the inductance of the chip capacitor 620 embeddedin the core substrate, and the inductance of the chip capacitor mountedon the back surface of the printed circuit board (on the surface at theside of daughter board) are shown as follows.

In the case of a single capacitor:

A capacitor of embedded type: 137 pH

A capacitor of back surface mounted type: 287 pH

In the case of eight capacitors connected in parallel:

Capacitors of embedded type: 60 pH

Capacitors of back surface mounted type: 72 pH

In both cases where a single capacitor is used and where a plurality ofcapacitors are connected in parallel to obtain an increased capacity, aninductance can be lowered by incorporating the chip capacitor.

Hereinafter, the results of reliability test will be described. In thetest, the rate of change in the electrostatic capacity of a single chipcapacitor in the printed circuit board of the sixth modification wasmeasured.

Rate of change in electrostatic capacity (measured at a frequency of 100Hz) (measured at a frequency of 1 kHz)

Steam 168 hours: 0.3% 0.4% HAST 100 hours: −0.9% −0.9% TS 1000 cycles:1.1% 1.3%

In the Steam test, the chip capacitor was subjected to steam to be keptat a humidity of 100%. In the HAST test, the chip capacitor was left for100 hours at a relative humidity of 100%, an applied voltage of 1.3V,and at a temperature of 121° C. In the TS test, the chip capacitor waslest for 30 minutes at 125° C., and 30 minutes at 55° C., and this testwas repeated 1000 times.

In the above-described reliability test, it was realized that theprinted circuit board incorporating the chip capacitor attains areliability of the same level as the conventional printed capacitor onwhich a capacitor is mounted on its surface. As described above, in theTS test, even if an internal stress is generated due to the differencein the thermal expansion coefficients between the capacitor made ofceramic, and the core substrate and the resin interlayer insulatinglayer made of resin, no problems are created such as a disconnectionbetween the terminals of the chip capacitors and the via holes, andpeeling of the chip capacitors from the interlayer resin insulatinglayer, and creation of cracks in the interlayer resin insulating layer.In this manner, high reliability can be attained over a long period oftime.

According to the structure of the fourth embodiment, there is no problemof lowering the electric characteristics caused by inductance.

The connection to the capacitors can be established from their bottomsurfaces. It can be said that this structure contributes to a shortenedloop inductance and an increased degree of freedom.

Since the resin is charged in the space between the core substrate andthe capacitor, even if the stress caused by the capacitors is generated,the stress can be alleviated. In addition, no migration is created. As aresult, neither peeling nor dissolution is caused between the electrodesof the capacitors and the connecting sections of the via holes. Due tothese arrangements, the desired performance can be maintained in thereliability test. In the case where the capacitor is coated with copper,the generation of migration can be prevented.

Fifth Embodiment

First, the structure of a printed circuit board according to a fifthembodiment of the present invention will be described with reference toFIGS. 63 and 64. FIG. 63 is a diagram showing a cross section of aprinted circuit board 810. FIG. 64 is a diagram showing the state wherean IC chip 890 is mounted on the printed circuit board 810 shown in FIG.63, and the printed circuit board 810 is attached to a daughter board894.

As shown in FIG. 63, the printed circuit board 810 incorporates chipcapacitors 820, a core substrate 830 for accommodating the chipcapacitors 820, and an interlayer resin insulating layer 850constituting the buildup layers 880A, 880B. The core substrate 830 isconstituted by an accommodating layer 830 a for accommodating thecapacitor 820, and a connection layer 840. Via holes 860 and a conductorcircuit 858 are formed in the connection layer 840. Via holes 960 and aconductor circuit 958 are formed in the interlayer resin insulatinglayer 850. In this embodiment, the buildup layer is constituted by asingle interlayer resin insulating layer 850. As an alternative to this,the buildup layer may be constituted by a plurality of interlayer resininsulating layers.

As shown in FIG. 66(A). the chip capacitor 820 is constituted by a firstelectrode 821, a second electrode 822, and a dielectric body 823interposed between the first and second electrodes. The dielectric body823 includes a plurality of first conductive films 824 connected to thefirst electrode 821 and a plurality of second conductive films 825connected to the second electrode 822 in an opposed relation to eachother. The first electrode 821 and the second electrode 822 arerespectively coated with a metal layer 826 metallized with copper, andfurther coated with a coating layer 828 such as solder on the metallayer 826. In this embodiment, a connection for the first electrode 821and the second electrode 822 is established by via holes 860 made ofplating. In the printed circuit board according to the fifth embodiment,as shown in FIG. 66(B), the metal layer 826 is exposed from the coatinglayer 828 formed on the first and second electrodes 821, 822. With thisarrangement, as shown in FIG. 63, the connection between the first andsecond electrodes 821, 822 and the via holes 860 is increased, and theconnection resistance therebetween can be lowered.

On the surface of the dielectric body 823 made of ceramic of the chipcapacitor 820, a rough surface 823α is formed. The rough surface 823αcontributes to an increased adhesion between the chip capacitor 820 madeof ceramic and the connection layer 840 made of resin, thereby avoidingthe connection layer 840 from peeling from the interface with the chipcapacitor 820 even when a heat cycle test is conducted. The roughsurface 823 α can be formed by polishing the surface of the chipcapacitor 820 after the sintering step, or by roughening the surface ofthe chip capacitor 20 before the sintering step.

As shown in FIG. 64, the via holes 960 in the upper buildup layer 880Aare formed with bumps 876 to be respectively connected to pads 892S1,892S2, 892P1, 892P2 of the IC chip 890. On the other hand, the via holes960 in the lower buildup layer 880B are formed with bumps 876 to berespectively connected to pads 895S1, 895S2, 895P1, 895P2. Through holes846 are formed in the core substrate 830.

The pad 892S2 for signal of the IC chip 890 is connected to the pad895S2 for signal of the daughter board 894 through he bump 876-theconductor circuit 958-the via hole 960-the through hole 846-the via hole960-the bump 876. On the other hand, the pad 892S1 for signal of the ICchip 890 is connected to the pad 895S1 for signal of the daughter board894 through the bump 876-the via hole 960-the through hole 846-the viahole 960-the bump 876.

The pad 892P1 for power supply of the IC chip 890 is connected to thefirst electrode 821 of the chip capacitor 820 through the bump 876-viahole 960-the conductor circuit 858-the via hole 860. On the other hand,the pad 895P1 for power supply of the daughter board 894 is connected tothe first electrode 821 of the chip capacitor 820 through the bump876-the via hole 960-the through hole 846-the conductor circuit 858-thevia hole 860.

The pad 892P2 for power supply of the IC chip 890 is connected to thesecond electrode 822 of the chip capacitor 820 through the bump 876-thevia hole 960-the conductor circuit 858-the via hole 860. On the otherhand, the pad 895P2 for power supply of the daughter board 894 isconnected to the second electrode 822 of the chip capacitor 820 throughthe bump 876-the via hole 960-the through hole 846-the conductor circuit858-the via hole 860.

In the printed circuit board 810 of this embodiment, the chip capacitors820 are placed immediately below the IC chip 890. The distance from theIC chip to each capacitor is shortened, and therefore, electric powercan be instantaneously supplied to the IC chip. That is, the loop lengthwhich determines the loop inductance can be shortened.

In addition, the through hole 846 is formed between the chip capacitors820, and no signal line passes through the chip capacitors 820. In thisstructure, there is no problem that the impedance becomes discontinuousby the high dielectric body to generate a reflection, and that thetransmission is delayed by passing through the high dielectric body.

The external substrate (i.e. daughter board) 894 to be connected to theback surface of the printed circuit board is connected to the firstelectrode 821 and the second electrode 822 of the capacitor 820 throughthe via holes 860 formed in the connection layer 840 on the side of ICchip and the through holes 846 formed in the core substrate 830. Thatis, although the accommodation layer 830 a having a core material ishard to process, though holes are formed in the accommodation layer 830a so that the terminals of the capacitors are not directly connected tothe outside surface. As a result, the reliability of the connection canbe increased.

In this embodiment, as shown in FIG. 63, an adhesive 836 is interposedbetween the lower surface of the penetrating openings 837 of the coresubstrate 830 and the chip capacitor 820. In addition, a resin fillingagent 836 a is charged in a space between the side surface of thepenetrating openings 837 and the chip capacitor 820. The thermalexpansion coefficients of the resin layer 836 and the resin fillingagent 836 a provided on the bottom surface of the chip capacitor 820 areset to the values lower than those of the core substrate 830 and theconnection layer 840, that is, are set to the values close to that ofthe chip capacitor 820 made of ceramics. In this manner, even ifinternal stress is generated between the core substrate 830 and theconnection layer 840, and the chip capacitor 820 caused by thedifference in the thermal expansion coefficients therebetween, cracksand peelings do not easily occur in the core substrate and theconnection layer 840. As a result, high reliability can be attained. Inaddition, the generation of migration can be prevented.

The process of manufacturing the printed circuit board of the fifthembodiment will be described with reference to FIGS. 60 to 63.

(1) Four prepregs 835 impregnated with an epoxy resin are laminated ontop of each other to form a laminated plate 832 a, and a penetratingopening 837 for accommodating a chip capacitor is formed in thelaminated plate 832 a. On the other hand, two prepregs 835 are laminatedon top of each other to form a laminated plate 832 b (FIG. 60(A)). Theprepreg 835 may be impregnated with, instead of the epoxy resin, BT,phenolic resin, or reinforcement material such as glass cloth. It isimpossible, however, to use substrates made of ceramic and AIN as thecore substrate. These substrates are poor in outer shape processingcharacteristics, and cannot accommodate capacitors in some cases. Inaddition, a space is created inside the substrate even if it is filledwith a resin. The laminated plate 832 a and the laminated plate 832 bare laminated to each other to form an accommodation layer 830 a. Then,as described above referring to FIG. 66(B), chip capacitors 820 fromwhich a coating layer 828 on the first and second electrodes 821, 822 ispeeled are accommodated (FIG. 60(B)). It is preferable that an adhesive836 is interposed between the penetrating openings 837 and the chipcapacitor 820. The resin and interlayer resin insulating layer used inthis invention has melting points of 300° C. or lower. Therefore, whenheat higher than 350° C. is applied, the resin and interlayer resininsulating layer may be dissolved, softened, or carbonized.

(2) The resin film 840 a (i.e. a connection layer) is laminated on bothsides of the accommodating layer constituted by the laminated plate 832a and the laminated plate 832 b and accommodating the chip capacitors820 (FIG. 60(C)), and are pressed from both sides to flatten thesurface. Then, heating and curing is conducted to form a core substrate830 constituted by the accommodating layer 830 a accommodating the chipcapacitors 820 and the connection layer 840 (FIG. 60(D)). In thisembodiment, the accommodating layer 830 a which accommodates thecapacitors 820 and the connection layer 840 are bonded to each other byapplication of pressure from both sides to form the core substrate 830.As a result, the core substrate 830 has a flat surface. The interlayerresin insulating layer 850 and the conductor circuit 958 can belaminated in a later step in such a manner that high reliability isattained.

(3) It is preferable that a resin filling agent 836 a is charged in theside surface of the penetrating openings 837 of the core substrate toincrease the air tightness. In this embodiment, the resin film 840 a maybe a resin film of the same type as that used in the first embodimentwhich has no metal layer. As an alternative to this, a resin film (RCC)having a metal layer on its one side may be used. That is, it ispossible to use a both-sided plate, a one-sided plate, a resin platehaving no metal film, and a resin film.

(4) Penetrating openings 846 a each having a diameter of 300 to 500 μmfor through hole are formed in the core substrate and the interlayerresin insulating layer 850 with a drill (FIG. 61(A)). Non-penetratingopenings 848 extending to the first and second electrodes 821, 822 areformed in the upper interlayer resin insulating layer 850 by CO2 laser,YAG laser, excimer laser, or UV laser (FIG. 61(B)). As the case may be,an area mask on which through holes are penetrated at positionscorresponding to the positions of the non-penetrating openings ismounted, and an area processing is conducted by a laser. In the casewhere it is desired to form via holes having different sizes anddiameter from each other, the lasers may be used to form the via holes.

(5) A desmear process is performed. Subsequently, a palladium catalystis provided to the substrate 830, and then, the core substrate 830 isimmersed into an electroless plating solution to cause the electrolessplated film to uniformly precipitate an electroless plated film 852(FIG. 61(C)). As a result of this, a rough layer can be formed on thesurface of the electroless copper plated film 852. The rough surface hasRa (mean roughness height) of 0.01 to 5 μm, and especially preferable isRa of 0.5 to 3 μm.

(6) A photosensitive dry film is attached on the surface of theelectroless plated film 852, and a mask is mounted thereon. Exposure tolight and development are performed to form a resist 854 having apredetermined pattern (FIG. 62(A)). In this embodiment, an electrolessplating is employed. Alternatively, a metal film of copper, nickel andthe like may be formed by sputtering. The sputtering is disadvantageousfrom the viewpoint of cost, but is advantageous in that the adhesionwith the resin film can be improved. The core substrate 830 is immersedin an electrolytic plating solution, and a current is allowed to flow inthe core substrate 830 through the electroless plated film 852 toprecipitate an electrolytic copper plated film 856 (FIG. 62(B)). Theresist 854 is peeled by 5% KOH, and the electroless plated film 852below the resist 854 is etched with a mixed solution of sulfuric acidand hydrogen peroxide to be dissolved and removed. As a result, viaholes 860 are formed in the non-penetrating openings 848 of theconnection layer 840, a conductor circuit 858 is formed on the surfaceof the connection layer 840, and through holes 846 are formed in thepenetrating openings 846 a of the core substrate 830 (FIG. 62(C)). Thesubsequent processes are the same as the steps (10) to (15) of thesecond embodiment which has been described above, and therefore, theirdescription will be omitted.

The processes of mounting the IC chip on the printed circuit board, andattaching the printed circuit board to the daughter board are the sameas those of the first embodiment, and their description will be omitted.

First Modification of Fifth Embodiment

A printed circuit board according to a first modification of the fifthembodiment of this invention will be described with reference to FIG.65. In the printed circuit board of the first modification, conductivepins 896 are provided, and a connection with the daughter board isestablished through the conductive pins 896. A core substrate 830 isconstituted by an accommodation layer 830 a having penetrating opening837, and connection layers 840 provided on both sides of theaccommodation layer 830 a. Via holes 860 for establishing connectionbetween the electrodes 821, 822 of the chip capacitors 820 and the ICchip 890 and the conductive pins 896 are formed in the connection layers840 provided on both sides of the accommodation layer 830 a. In thisfirst modification, as shown in FIG. 66(C), the coating of theelectrodes 821, 822 of the chip capacitors 820 is completely removed.

Whereas in the fifth embodiment described above, chip capacitors 820 areaccommodated in the core substrate 830 alone, in the first modification,chip capacitors 920 each having a large capacity are mounted on thefront surface and back surface of the core substrate 830.

The IC chip conducts a complicated calculation, and in the calculationprocessing, it instantaneously consumes a large electric power. In orderto provide a large electric power to the IC chip, in the firstmodification, chip capacitors 820 for power supply and chip capacitors920 are provided to the printed circuit board. The effect of providingthe chip capacitors 820 and 920 is the same as that attained in thefourth modification of the first embodiment, and therefore, itsdescription will be omitted.

Second Modification of Fifth Embodiment

A printed circuit board according to a second modification of the fifthembodiment will be described referring to FIGS. 67 and 68.

The printed circuit board according to the second modification has thesimilar structure as of the fifth embodiment described above, except forthe following points. That is, in the fifth embodiment, the coating ofthe electrodes 821, 822 of the chip capacitors 820 is partially peeledoff to cause the surface of the metal layer 826 to be uncoated andexposed to the outside. Contrary to this, in the printed circuit boardaccording to the second modification, in the chip capacitor 820, asshown in FIG. 68(A), the coating of the metal layer 826 is completelypeeled, and then as shown in FIG. 68(B), a copper plated film 829 iscoated on the surface of the metal layer 826. The coating of the platedfilm may be made of plating such as electrolytic plating and electrolessplating. An electric connection for the first and second electrodes 821,822 coated with the copper plated film 829 is established through viaholes 860 constituted by a copper plating. The electrodes 821, 822 ofthe chip capacitor are metallized and has pits and projections on theirsurfaces. Therefore, the resin may be left in the pits and projectionsin the step of forming non-penetrating openings 848 in the connectionlayer 840 of the fifth embodiment shown in FIG. 61(B). The resin left inthe pits and projections may cause a disconnection between the first andsecond electrodes 821, 822 and the via holes 860. Contrary to this, inthe second modification, the surfaces of the first and second electrodes821, 822 coated with the copper plated film 829 are flat and smooth.When the penetrating openings 848 are formed in the connection layer 840formed on the electrodes, no resin is left on the surfaces of theelectrodes 821, 822. When the via holes 860 are formed, the connectionbetween the via holes 860 and the electrodes 821, 822 has increasedreliability.

Since the via holes 860 are made by plating into the electrodes 821, 822formed with the copper plated film 829, the electrodes 821, 822 arefirmly connected to the via holes 860. No disconnection occurs betweenthe electrodes 821, 822 and via holes 860 even when a heat cycle test isconducted.

The copper plated film 829 is formed after removing the coating layer828 in the step of accommodating the chip capacitors in the printedcircuit board. Alternatively, the copper plated film 829 may be directlyprovided onto the surface of the metal layer 826 in the step ofmanufacturing the chip capacitor 820. In the second modification,openings which extend to the copper plated film 829 of the electrodesare formed by a laser, and then a desmear process is performed to formvia holes by copper plating. Therefore, even if an oxide film is formedon the surface of the copper plated film 829, the oxide film can beremoved in the laser or desmear process. In this manner, the first andsecond electrodes 821, 822 can be properly connected to the via holes860.

On the surface of the dielectric body 823 made of ceramic of the chipcapacitor 820, a rough surface 823α may be formed. The rough surface823α contributes to an increased adhesion between the chip capacitor 820made of ceramic and the connection layer 840 made of resin, therebyavoiding the connection layer 840 from peeling from the interface withthe chip capacitor 820 even when a heat cycle test is conducted.

Third Modification of Fifth Embodiment

A structure of a printed circuit board according to a third modificationof the fifth embodiment will be described referring to FIGS. 69 and 18.

The printed circuit board 810 according to the third modification hasthe structure similar to that of the fifth embodiment, except for thestructure of the chip capacitors 20 accommodated in the core substrate830. FIG. 18 is a plan view showing the chip capacitors. FIG. 18(A) is adiagram showing a chip capacitor before being cut from which a pluralityof pieces are to be obtained by cutting. In FIG. 18(A), a chain lineshows the cutting line. In the printed circuit board described in thethird modification, as shown in the plan view of FIG. 18(B), the firstelectrodes 21 and the second electrodes 22 are provide along the sideends of the chip capacitor. FIG. 18(C) is a diagram showing a chipcapacitor before being cut from which a plurality of pieces are to beobtained by cutting according to the third modification. In FIG. 18(C),a chain line shows the cutting line. In the printed circuit boarddescribed in the third modification, as shown in the plan view of FIG.18(D), the first electrodes 21 and the second electrodes 22 are provideinside the side ends of the chip capacitor.

In the third modification, the printed circuit board has a chipcapacitor 20 in which the electrodes are formed along an inside of theouter edge thereof. Therefore, a chip capacitor having a large capacitycan be used as the chip capacitor 20. In the third modification, thesurface of the chip capacitors are subjected to roughening process.

Fourth Modification of Fifth Embodiment

A printed circuit board according to a fourth modification of thepresent invention will be described referring to FIGS. 70 and 19.

FIG. 70 is a diagram showing a cross section of a printed circuit board810 according to the fourth modification. FIG. 68 is a diagram showing aplan view of the chip capacitor 20 to be accommodated in the coresubstrate 830 of the printed circuit board 810. In the above-describedfifth embodiment, a plurality of chip capacitors each having a smallcapacity are accommodated in the core substrate. Contrary to this, inthe fourth modification, a large chip capacitor 20 having a largecapacity and having electrodes formed in matrix is accommodated in thecore substrate 830. The chip capacitor 20 includes first electrodes 21,second electrodes 22, a dielectric body 23, a first conductive film 24connected to the first electrodes 21, a second conductive film 25connected to the second electrodes 22, and electrodes 27 which are notconnected to the first conductive film 24 and the second conductive film25 and used for connecting the upper and lower surfaces of the chipcapacitor. The chip capacitor is connected to the IC chip and thedaughter board through the electrodes 27.

In the printed circuit board according to the fourth modification, thechip capacitor 20 having a large size is used. Therefore, a chipcapacitor having a large capacity can be employed as the chip capacitor20. In addition, the use of large-sized chip capacitor 20 prevents thewarpage of the printed circuit board even if the printed circuit boardis repeatedly subjected to heat cycle. In the fourth modification, thesurface of the chip capacitors are subjected to roughening process.

Fifth Modification of Fifth Embodiment

A printed circuit board according to a fifth modification will bedescribed referring to FIGS. 71 and 20. FIG. 71 is a diagram showing across section of the printed circuit board. FIG. 20(A) is a diagramshowing a chip capacitor before being cut from which a plurality ofpieces are to be obtained by cutting. In FIG. 20(A), a chain line showsan ordinary cutting line. FIG. 20(B) is a diagram showing a plan view ofthe chip capacitor. As shown in FIG. 20(B), a plurality of chipcapacitors from each of which a plurality of pieces are to be obtainedby cutting (in FIG. 20(B), three pieces) are connected into one pieceunit having a large size.

In the fifth modification, the chip capacitor 20 having a large size isused. Therefore, a chip capacitor having a large capacity can beemployed as the chip capacitor 20. In addition, the use of large-sizedchip capacitor 20 prevents the warpage of the printed circuit board 810even if the printed circuit board is repeatedly subjected to heat cycle.In the fifth modification, the surface of the chip capacitors aresubjected to roughening process.

Sixth Modification of Fifth Embodiment

A printed circuit board according to a sixth modification will bedescribed with reference to FIG. 72. FIG. 72 is a diagram showing across section of the printed circuit board. In the fifth modificationdescribed referring to FIG. 63, one chip capacitor 820 is accommodatedin the cavity 832 of the core substrate 830. Contrary to this, in thesixth modification, a plurality of chip capacitors 820 are accommodatedin the cavity 832. In the sixth modification, the chip capacitors can beincorporated in the core substrate with high density. In the sixthmodification, the surface of the chip capacitors is subjected toroughening process.

In the above-described embodiment, the chip capacitor is incorporated inthe printed circuit board. Instead of the chip capacitor, it is alsopossible to use a plate-like capacitor in which a conductive film isformed on a ceramic plate. In this embodiment, the surface of the chipcapacitor is roughened to increase its adhesion with the resininsulating layer. Alternatively, the surface of the chip capacitor maybe subjected to silane coupling process.

As to the printed circuit board of the second modification, theinductance of the chip capacitor 20 embedded in the core substrate, andthe inductance of the chip capacitor mounted on the back surface of theprinted circuit board (on the surface at the side of daughter board) areshown as follows.

In the case of a single capacitor:

A capacitor of embedded type: 137 pH

A capacitor of back surface mounted type: 287 pH

In the case of eight capacitors connected in parallel:

Capacitors of embedded type: 60 pH

Capacitors of back surface mounted type: 72 pH

In both cases where a single capacitor is used and where a plurality ofcapacitors are connected in parallel to obtain an increased capacity, aninductance can be lowered by incorporating the chip capacitor.

Hereinafter, the results of reliability test will be described. In thetest, the rate of change in the electrostatic capacity of a single chipcapacitor in the printed circuit board of the second modification wasmeasured.

Rate of change in electrostatic capacity (measured at a frequency of 100Hz) (measured at a frequency of 1 kHz)

Steam 168 hours: 0.3% 0.4% HAST 100 hours: −0.9% −0.9% TS 1000 cycles:1.1% 1.3%

In the Steam test, the chip capacitor was subjected to steam to be keptat a humidity of 100%. In the HAST test, the chip capacitor was left for100 hours at a relative humidity of 100%, an applied voltage of 1.3V,and at a temperature of 121° C. In the TS test, the chip capacitor wasleft for 30 minutes at 125° C., and 30 minutes at 55° C., and this testwas repeated 1000 times.

In the above-described reliability test, it was realized that theprinted circuit board incorporating the chip capacitor attains areliability of the same level as the conventional printed capacitor onwhich a capacitor is mounted on its surface. As described above, in theTS test, even if an internal stress is generated due to the differencein the thermal expansion coefficients between the capacitor made ofceramic, and the core substrate and the interlayer resin insulatinglayer made of resin, no problems are created such as a disconnectionbetween the terminals of the chip capacitors and the via holes, apeeling of the chip capacitors from the interlayer resin insulatinglayer, and the cracks in the interlayer resin insulating layer. In thismanner, high reliability can be attained over a long period of time.

According to the structure of the fifth embodiment, there is no problemof lowering the electric characteristics caused by inductance.

Under the conditions of the reliability test, neither deterioration inelectric characteristics nor peeling and cracks in the printed circuitboard are caused. Therefore, no problems are created between the chipcapacitors and the via holes.

Since the resin is charged in the space between the core substrate andthe capacitor, even if the stress caused by the capacitors is generated,the stress can be alleviated. In addition, no migration is created. As aresult, neither peeling nor dissolution is caused between the electrodesof the capacitors and the connecting sections of the via holes. Due tothese arrangements, the desired performance can be maintained in thereliability test.

In the case where the capacitor is coated with copper, the generation ofmigration can be prevented.

1. A printed circuit board comprising: an accommodating layer comprisingan insulating material and having a through opening extending between afirst surface of the accommodating layer and a second surface of theaccommodating layer on an opposite side of the first surface; a chipcapacitor accommodated in the through opening of the accommodating layerand comprising a first electrode structure, a second electrode structureand a dielectric body interposed between the first electrode structureand the second electrode structure, the first electrode structurecomprising a first electrode and a metal film coated on a surface of thefirst electrode, the second electrode structure comprising a secondelectrode and a metal film coated on a surface of the second electrode;a first connection layer formed over the first surface of theaccommodating layer and having a first via hole opening extending to themetal film of the first electrode structure and a second via holeopening extending to the metal film of the second electrode structure; asecond connection layer formed over the second surface of theaccommodating layer such that the chip capacitor is positioned betweenthe first connection layer and the second connection layer; a first viahole structure formed in the first via hole opening of the firstconnection layer and connected to the metal film of the first electrodestructure of the chip capacitor; and a second via hole structure formedin the second via hole opening of the first connection layer andconnected to the metal film of the second electrode structure of thechip capacitor.
 2. The printed circuit board according to claim 1,wherein the metal film formed on at least one of the first and secondelectrodes comprises a copper plated film.
 3. The printed circuit boardaccording to claim 1, wherein the chip capacitor has a roughenedsurface.
 4. The printed circuit board according to claim 1, wherein thefirst via hole structure in the first connection layer comprises acopper plating.
 5. The printed circuit board according to claim 1,wherein the first connection layer comprises a resin film formed bycuring a resin film which does not have a core material.
 6. The printedcircuit board according to claim 1, wherein the accommodating layercomprises a resin substrate comprising a core material impregnated witha resin.
 7. The printed circuit board according to claim 1, furthercomprising a third via hole structure, wherein the second connectionlayer has a third via hole opening extending to the metal film of one ofthe first and second electrode structures, and the third via holestructure is formed in the third via hole opening of the secondconnection layer.
 8. The printed circuit board according to claim 1,further comprising: an interlayer insulating layer formed over the firstconnection layer and having at least one via hole opening extending tothe first via hole structure; and at least one via hole structure formedin the at least one via hole opening of the interlayer insulating layer.9. The printed circuit board according to claim 1, further comprising: athird via hole structure; and a fourth via hole structure, wherein thesecond connection layer has a third via hole opening extending to themetal film of the first electrode structure, the third via holestructure is formed in the third via hole opening of the secondconnection layer, the second connection layer has a fourth via holeopening extending to the metal film of the second electrode structure,and the fourth via hole structure is formed in the fourth via holeopening of the second connection layer.
 10. The printed circuit boardaccording to claim 8, wherein the metal film formed on at least one ofthe first and second electrodes comprises a copper plated film.
 11. Theprinted circuit board according to claim 8, wherein the chip capacitorhas a roughened surface.
 12. The printed circuit board according toclaim 8, wherein the first via hole structure in the first connectionlayer comprises a copper plating.
 13. The printed circuit boardaccording to claim 8, wherein the first connection layer comprises aresin film formed by curing a resin film which does not have a corematerial.
 14. The printed circuit board according to claim 8, whereinthe accommodating layer comprises a resin substrate comprising a corematerial impregnated with a resin.
 15. The printed circuit boardaccording to claim 9, wherein the metal film formed on at least one ofthe first and second electrodes comprises a copper plated film.
 16. Theprinted circuit board according to claim 9, wherein each of the firstvia hole structure, the second via hole structure, the third via holestructure and the fourth via hole structure comprises a copper plating.